Series comparison

The kernel ABI for this is (finally) close to being merged:

https://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git/log/?h=for-next/bti-user

I've made a couple of tweaks from v8:

(1) Only map the interpreter or a static executable with BTI.
     The interpreter is responsible for handling the pages of
     a dynamic executable.  This is a behaviour change in the
     kernel ABI since the last time I audited the code.

(2) Rely on the recently released gcc 10 for building the test case.
     Thanks to Alex for helping me get a docker setup for that.

Based-on: <20200519185645.3915-1-richard.henderson@linaro.org>
("linux-user: mmap/mprotect prot values")

Based-on: An unpublished version of stsquad's testing/next

So for avoidance of doubt, the complete tree may be found at

https://github.com/rth7680/qemu/tree/tgt-arm-bti

Richard Henderson (5):
  linux-user/aarch64: Reset btype for signals
  linux-user: Set PAGE_TARGET_1 for TARGET_PROT_BTI
  include/elf: Add defines related to GNU property notes for AArch64
  linux-user: Parse NT_GNU_PROPERTY_TYPE_0 notes
  tests/tcg/aarch64: Add bti smoke test

include/elf.h                     |  22 +++++
 include/exec/cpu-all.h            |   2 +
 linux-user/qemu.h                 |   4 +
 linux-user/syscall_defs.h         |   4 +
 linux-user/aarch64/signal.c       |  10 ++-
 linux-user/elfload.c              | 143 ++++++++++++++++++++++--------
 linux-user/mmap.c                 |  16 ++++
 target/arm/translate-a64.c        |   6 +-
 tests/tcg/aarch64/bti-1.c         |  62 +++++++++++++
 tests/tcg/aarch64/bti-crt.inc.c   |  51 +++++++++++
 tests/tcg/aarch64/Makefile.target |   7 ++
 tests/tcg/configure.sh            |   4 +
 12 files changed, 291 insertions(+), 40 deletions(-)
 create mode 100644 tests/tcg/aarch64/bti-1.c
 create mode 100644 tests/tcg/aarch64/bti-crt.inc.c

-- 
2.20.1

The kernel sets btype for the signal handler as if for a call.

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
---
 linux-user/aarch64/signal.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/linux-user/aarch64/signal.c b/linux-user/aarch64/signal.c
index XXXXXXX..XXXXXXX 100644
--- a/linux-user/aarch64/signal.c
+++ b/linux-user/aarch64/signal.c
@@ -XXX,XX +XXX,XX @@ static void target_setup_frame(int usig, struct target_sigaction *ka,
             + offsetof(struct target_rt_frame_record, tramp);
     }
     env->xregs[0] = usig;
-    env->xregs[31] = frame_addr;
     env->xregs[29] = frame_addr + fr_ofs;
-    env->pc = ka->_sa_handler;
     env->xregs[30] = return_addr;
+    env->xregs[31] = frame_addr;
+    env->pc = ka->_sa_handler;
+
+    /* Invoke the signal handler as if by indirect call.  */
+    if (cpu_isar_feature(aa64_bti, env_archcpu(env))) {
+        env->btype = 2;
+    }
+
     if (info) {
         tswap_siginfo(&frame->info, info);
         env->xregs[1] = frame_addr + offsetof(struct target_rt_sigframe, info);
-- 
2.20.1

Transform the prot bit to a qemu internal page bit, and save
it in the page tables.

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
---
 include/exec/cpu-all.h     |  2 ++
 linux-user/syscall_defs.h  |  4 ++++
 linux-user/mmap.c          | 16 ++++++++++++++++
 target/arm/translate-a64.c |  6 +++---
 4 files changed, 25 insertions(+), 3 deletions(-)

diff --git a/include/exec/cpu-all.h b/include/exec/cpu-all.h
index XXXXXXX..XXXXXXX 100644
--- a/include/exec/cpu-all.h
+++ b/include/exec/cpu-all.h
@@ -XXX,XX +XXX,XX @@ extern intptr_t qemu_host_page_mask;
 /* FIXME: Code that sets/uses this is broken and needs to go away.  */
 #define PAGE_RESERVED  0x0020
 #endif
+/* Target-specific bits that will be used via page_get_flags().  */
+#define PAGE_TARGET_1  0x0080
 
 #if defined(CONFIG_USER_ONLY)
 void page_dump(FILE *f);
diff --git a/linux-user/syscall_defs.h b/linux-user/syscall_defs.h
index XXXXXXX..XXXXXXX 100644
--- a/linux-user/syscall_defs.h
+++ b/linux-user/syscall_defs.h
@@ -XXX,XX +XXX,XX @@ struct target_winsize {
 #define TARGET_PROT_SEM         0x08
 #endif
 
+#ifdef TARGET_AARCH64
+#define TARGET_PROT_BTI         0x10
+#endif
+
 /* Common */
 #define TARGET_MAP_SHARED	0x01		/* Share changes */
 #define TARGET_MAP_PRIVATE	0x02		/* Changes are private */
diff --git a/linux-user/mmap.c b/linux-user/mmap.c
index XXXXXXX..XXXXXXX 100644
--- a/linux-user/mmap.c
+++ b/linux-user/mmap.c
@@ -XXX,XX +XXX,XX @@ static int validate_prot_to_pageflags(int *host_prot, int prot)
     *host_prot = (prot & (PROT_READ | PROT_WRITE))
                | (prot & PROT_EXEC ? PROT_READ : 0);
 
+#ifdef TARGET_AARCH64
+    /*
+     * The PROT_BTI bit is only accepted if the cpu supports the feature.
+     * Since this is the unusual case, don't bother checking unless
+     * the bit has been requested.  If set and valid, record the bit
+     * within QEMU's page_flags as PAGE_TARGET_1.
+     */
+    if (prot & TARGET_PROT_BTI) {
+        ARMCPU *cpu = ARM_CPU(thread_cpu);
+        if (cpu_isar_feature(aa64_bti, cpu)) {
+            valid |= TARGET_PROT_BTI;
+            page_flags |= PAGE_TARGET_1;
+        }
+    }
+#endif
+
     return prot & ~valid ? 0 : page_flags;
 }
 
diff --git a/target/arm/translate-a64.c b/target/arm/translate-a64.c
index XXXXXXX..XXXXXXX 100644
--- a/target/arm/translate-a64.c
+++ b/target/arm/translate-a64.c
@@ -XXX,XX +XXX,XX @@ static void disas_data_proc_simd_fp(DisasContext *s, uint32_t insn)
  */
 static bool is_guarded_page(CPUARMState *env, DisasContext *s)
 {
-#ifdef CONFIG_USER_ONLY
-    return false;  /* FIXME */
-#else
     uint64_t addr = s->base.pc_first;
+#ifdef CONFIG_USER_ONLY
+    return page_get_flags(addr) & PAGE_TARGET_1;
+#else
     int mmu_idx = arm_to_core_mmu_idx(s->mmu_idx);
     unsigned int index = tlb_index(env, mmu_idx, addr);
     CPUTLBEntry *entry = tlb_entry(env, mmu_idx, addr);
-- 
2.20.1

These are all of the defines required to parse
GNU_PROPERTY_AARCH64_FEATURE_1_AND, copied from binutils.
Other missing defines related to other GNU program headers
and notes are elided for now.

Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
---
 include/elf.h | 22 ++++++++++++++++++++++
 1 file changed, 22 insertions(+)

diff --git a/include/elf.h b/include/elf.h
index XXXXXXX..XXXXXXX 100644
--- a/include/elf.h
+++ b/include/elf.h
@@ -XXX,XX +XXX,XX @@ typedef int64_t  Elf64_Sxword;
 #define PT_NOTE    4
 #define PT_SHLIB   5
 #define PT_PHDR    6
+#define PT_LOOS    0x60000000
+#define PT_HIOS    0x6fffffff
 #define PT_LOPROC  0x70000000
 #define PT_HIPROC  0x7fffffff
 
+#define PT_GNU_PROPERTY   (PT_LOOS + 0x474e553)
+
 #define PT_MIPS_REGINFO   0x70000000
 #define PT_MIPS_RTPROC    0x70000001
 #define PT_MIPS_OPTIONS   0x70000002
@@ -XXX,XX +XXX,XX @@ typedef struct elf64_shdr {
 #define NT_ARM_SYSTEM_CALL      0x404   /* ARM system call number */
 #define NT_ARM_SVE      0x405           /* ARM Scalable Vector Extension regs */
 
+/* Defined note types for GNU systems.  */
+
+#define NT_GNU_PROPERTY_TYPE_0  5       /* Program property */
+
+/* Values used in GNU .note.gnu.property notes (NT_GNU_PROPERTY_TYPE_0).  */
+
+#define GNU_PROPERTY_STACK_SIZE                 1
+#define GNU_PROPERTY_NO_COPY_ON_PROTECTED       2
+
+#define GNU_PROPERTY_LOPROC                     0xc0000000
+#define GNU_PROPERTY_HIPROC                     0xdfffffff
+#define GNU_PROPERTY_LOUSER                     0xe0000000
+#define GNU_PROPERTY_HIUSER                     0xffffffff
+
+#define GNU_PROPERTY_AARCH64_FEATURE_1_AND      0xc0000000
+#define GNU_PROPERTY_AARCH64_FEATURE_1_BTI      (1u << 0)
+#define GNU_PROPERTY_AARCH64_FEATURE_1_PAC      (1u << 1)
+
 /*
  * Physical entry point into the kernel.
  *
-- 
2.20.1

For aarch64, this includes the GNU_PROPERTY_AARCH64_FEATURE_1_BTI bit,
which indicates that the image should be mapped with guarded pages.

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
---
v9: Only map the startup executable with BTI; anything else must be
    handled by the interpreter.
---
 linux-user/qemu.h    |   4 ++
 linux-user/elfload.c | 143 ++++++++++++++++++++++++++++++++-----------
 2 files changed, 112 insertions(+), 35 deletions(-)

diff --git a/linux-user/qemu.h b/linux-user/qemu.h
index XXXXXXX..XXXXXXX 100644
--- a/linux-user/qemu.h
+++ b/linux-user/qemu.h
@@ -XXX,XX +XXX,XX @@ struct image_info {
         abi_ulong       interpreter_loadmap_addr;
         abi_ulong       interpreter_pt_dynamic_addr;
         struct image_info *other_info;
+
+        /* For target-specific processing of NT_GNU_PROPERTY_TYPE_0. */
+        uint32_t        note_flags;
+
 #ifdef TARGET_MIPS
         int             fp_abi;
         int             interp_fp_abi;
diff --git a/linux-user/elfload.c b/linux-user/elfload.c
index XXXXXXX..XXXXXXX 100644
--- a/linux-user/elfload.c
+++ b/linux-user/elfload.c
@@ -XXX,XX +XXX,XX @@ static void load_elf_image(const char *image_name, int image_fd,
     struct elfhdr *ehdr = (struct elfhdr *)bprm_buf;
     struct elf_phdr *phdr;
     abi_ulong load_addr, load_bias, loaddr, hiaddr, error;
-    int i, retval;
+    int i, retval, prot_exec;
     const char *errmsg;
 
     /* First of all, some simple consistency checks */
@@ -XXX,XX +XXX,XX @@ static void load_elf_image(const char *image_name, int image_fd,
     loaddr = -1, hiaddr = 0;
     info->alignment = 0;
     for (i = 0; i < ehdr->e_phnum; ++i) {
-        if (phdr[i].p_type == PT_LOAD) {
-            abi_ulong a = phdr[i].p_vaddr - phdr[i].p_offset;
+        struct elf_phdr *eppnt = phdr + i;
+
+        if (eppnt->p_type == PT_LOAD) {
+            abi_ulong a = eppnt->p_vaddr - eppnt->p_offset;
             if (a < loaddr) {
                 loaddr = a;
             }
-            a = phdr[i].p_vaddr + phdr[i].p_memsz;
+            a = eppnt->p_vaddr + eppnt->p_memsz;
             if (a > hiaddr) {
                 hiaddr = a;
             }
             ++info->nsegs;
-            info->alignment |= phdr[i].p_align;
+            info->alignment |= eppnt->p_align;
+        } else if (eppnt->p_type == PT_INTERP && pinterp_name) {
+            char *interp_name;
+
+            if (*pinterp_name) {
+                errmsg = "Multiple PT_INTERP entries";
+                goto exit_errmsg;
+            }
+            interp_name = malloc(eppnt->p_filesz);
+            if (!interp_name) {
+                goto exit_perror;
+            }
+
+            if (eppnt->p_offset + eppnt->p_filesz <= BPRM_BUF_SIZE) {
+                memcpy(interp_name, bprm_buf + eppnt->p_offset,
+                       eppnt->p_filesz);
+            } else {
+                retval = pread(image_fd, interp_name, eppnt->p_filesz,
+                               eppnt->p_offset);
+                if (retval != eppnt->p_filesz) {
+                    goto exit_perror;
+                }
+            }
+            if (interp_name[eppnt->p_filesz - 1] != 0) {
+                errmsg = "Invalid PT_INTERP entry";
+                goto exit_errmsg;
+            }
+            *pinterp_name = interp_name;
+        } else if (eppnt->p_type == PT_GNU_PROPERTY) {
+            /* Process NT_GNU_PROPERTY_TYPE_0. */
+            const uint32_t gnu0_magic = const_le32('G' | 'N' << 8 | 'U' << 16);
+            uint32_t note[7];
+
+            /*
+             * The note contents are 7 words, but depending on LP64 vs ILP32
+             * there may be an 8th padding word at the end.  Check for and
+             * read the minimum size.  Further checks below will validate
+             * that the sizes of everything involved are as we expect.
+             */
+            if (eppnt->p_filesz < sizeof(note)) {
+                continue;
+            }
+            if (eppnt->p_offset + eppnt->p_filesz <= BPRM_BUF_SIZE) {
+                memcpy(note, bprm_buf + eppnt->p_offset, sizeof(note));
+            } else {
+                retval = pread(image_fd, note, sizeof(note), eppnt->p_offset);
+                if (retval != sizeof(note)) {
+                    goto exit_perror;
+                }
+            }
+#ifdef BSWAP_NEEDED
+            for (i = 0; i < ARRAY_SIZE(note); ++i) {
+                bswap32s(note + i);
+            }
+#endif
+            /*
+             * Check that this is a NT_GNU_PROPERTY_TYPE_0 note.
+             * Again, descsz includes padding.  Full size validation
+             * awaits checking the final payload.
+             */
+            if (note[0] != 4 ||                       /* namesz */
+                note[1] < 12 ||                       /* descsz */
+                note[2] != NT_GNU_PROPERTY_TYPE_0 ||  /* type */
+                note[3] != gnu0_magic) {              /* name */
+                continue;
+            }
+#ifdef TARGET_AARCH64
+            if (note[4] == GNU_PROPERTY_AARCH64_FEATURE_1_AND &&
+                note[5] == 4) {
+                info->note_flags = note[6];
+            }
+#endif /* TARGET_AARCH64 */
         }
     }
 
@@ -XXX,XX +XXX,XX @@ static void load_elf_image(const char *image_name, int image_fd,
     info->brk = 0;
     info->elf_flags = ehdr->e_flags;
 
+    prot_exec = PROT_EXEC;
+#ifdef TARGET_AARCH64
+    /*
+     * If the BTI feature is present, this indicates that the executable
+     * pages of the startup binary should be mapped with PROT_BTI, so that
+     * branch targets are enforced.
+     *
+     * The startup executable is either the interpreter or the static
+     * binary.  The interpreter is responsible for all pages of a
+     * dynamic executable.
+     *
+     * Elf notes are backward compatible to older cpus.
+     * Do not enable BTI unless it is supported.
+     */
+    if ((info->note_flags & GNU_PROPERTY_AARCH64_FEATURE_1_BTI)
+        && (pinterp_name == NULL || *pinterp_name == 0)
+        && cpu_isar_feature(aa64_bti, ARM_CPU(thread_cpu))) {
+        prot_exec |= TARGET_PROT_BTI;
+    }
+#endif
+
     for (i = 0; i < ehdr->e_phnum; i++) {
         struct elf_phdr *eppnt = phdr + i;
         if (eppnt->p_type == PT_LOAD) {
             abi_ulong vaddr, vaddr_po, vaddr_ps, vaddr_ef, vaddr_em, vaddr_len;
             int elf_prot = 0;
 
-            if (eppnt->p_flags & PF_R) elf_prot =  PROT_READ;
-            if (eppnt->p_flags & PF_W) elf_prot |= PROT_WRITE;
-            if (eppnt->p_flags & PF_X) elf_prot |= PROT_EXEC;
+            if (eppnt->p_flags & PF_R) {
+                elf_prot |= PROT_READ;
+            }
+            if (eppnt->p_flags & PF_W) {
+                elf_prot |= PROT_WRITE;
+            }
+            if (eppnt->p_flags & PF_X) {
+                elf_prot |= prot_exec;
+            }
 
             vaddr = load_bias + eppnt->p_vaddr;
             vaddr_po = TARGET_ELF_PAGEOFFSET(vaddr);
@@ -XXX,XX +XXX,XX @@ static void load_elf_image(const char *image_name, int image_fd,
                     info->brk = vaddr_em;
                 }
             }
-        } else if (eppnt->p_type == PT_INTERP && pinterp_name) {
-            char *interp_name;
-
-            if (*pinterp_name) {
-                errmsg = "Multiple PT_INTERP entries";
-                goto exit_errmsg;
-            }
-            interp_name = malloc(eppnt->p_filesz);
-            if (!interp_name) {
-                goto exit_perror;
-            }
-
-            if (eppnt->p_offset + eppnt->p_filesz <= BPRM_BUF_SIZE) {
-                memcpy(interp_name, bprm_buf + eppnt->p_offset,
-                       eppnt->p_filesz);
-            } else {
-                retval = pread(image_fd, interp_name, eppnt->p_filesz,
-                               eppnt->p_offset);
-                if (retval != eppnt->p_filesz) {
-                    goto exit_perror;
-                }
-            }
-            if (interp_name[eppnt->p_filesz - 1] != 0) {
-                errmsg = "Invalid PT_INTERP entry";
-                goto exit_errmsg;
-            }
-            *pinterp_name = interp_name;
 #ifdef TARGET_MIPS
         } else if (eppnt->p_type == PT_MIPS_ABIFLAGS) {
             Mips_elf_abiflags_v0 abiflags;
-- 
2.20.1

This test requires gcc 10 for -mbranch-protection=standard.

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
---
v9: Expect and require gcc 10.
---
 tests/tcg/aarch64/bti-1.c         | 62 +++++++++++++++++++++++++++++++
 tests/tcg/aarch64/bti-crt.inc.c   | 51 +++++++++++++++++++++++++
 tests/tcg/aarch64/Makefile.target |  7 ++++
 tests/tcg/configure.sh            |  4 ++
 4 files changed, 124 insertions(+)
 create mode 100644 tests/tcg/aarch64/bti-1.c
 create mode 100644 tests/tcg/aarch64/bti-crt.inc.c

diff --git a/tests/tcg/aarch64/bti-1.c b/tests/tcg/aarch64/bti-1.c
new file mode 100644
index XXXXXXX..XXXXXXX
--- /dev/null
+++ b/tests/tcg/aarch64/bti-1.c
@@ -XXX,XX +XXX,XX @@
+/*
+ * Branch target identification, basic notskip cases.
+ */
+
+#include "bti-crt.inc.c"
+
+static void skip2_sigill(int sig, siginfo_t *info, ucontext_t *uc)
+{
+    uc->uc_mcontext.pc += 8;
+    uc->uc_mcontext.pstate = 1;
+}
+
+#define NOP       "nop"
+#define BTI_N     "hint #32"
+#define BTI_C     "hint #34"
+#define BTI_J     "hint #36"
+#define BTI_JC    "hint #38"
+
+#define BTYPE_1(DEST) \
+    asm("mov %0,#1; adr x16, 1f; br x16; 1: " DEST "; mov %0,#0" \
+        : "=r"(skipped) : : "x16")
+
+#define BTYPE_2(DEST) \
+    asm("mov %0,#1; adr x16, 1f; blr x16; 1: " DEST "; mov %0,#0" \
+        : "=r"(skipped) : : "x16", "x30")
+
+#define BTYPE_3(DEST) \
+    asm("mov %0,#1; adr x15, 1f; br x15; 1: " DEST "; mov %0,#0" \
+        : "=r"(skipped) : : "x15")
+
+#define TEST(WHICH, DEST, EXPECT) \
+    do { WHICH(DEST); fail += skipped ^ EXPECT; } while (0)
+
+
+int main()
+{
+    int fail = 0;
+    int skipped;
+
+    /* Signal-like with SA_SIGINFO.  */
+    signal_info(SIGILL, skip2_sigill);
+
+    TEST(BTYPE_1, NOP, 1);
+    TEST(BTYPE_1, BTI_N, 1);
+    TEST(BTYPE_1, BTI_C, 0);
+    TEST(BTYPE_1, BTI_J, 0);
+    TEST(BTYPE_1, BTI_JC, 0);
+
+    TEST(BTYPE_2, NOP, 1);
+    TEST(BTYPE_2, BTI_N, 1);
+    TEST(BTYPE_2, BTI_C, 0);
+    TEST(BTYPE_2, BTI_J, 1);
+    TEST(BTYPE_2, BTI_JC, 0);
+
+    TEST(BTYPE_3, NOP, 1);
+    TEST(BTYPE_3, BTI_N, 1);
+    TEST(BTYPE_3, BTI_C, 1);
+    TEST(BTYPE_3, BTI_J, 0);
+    TEST(BTYPE_3, BTI_JC, 0);
+
+    return fail;
+}
diff --git a/tests/tcg/aarch64/bti-crt.inc.c b/tests/tcg/aarch64/bti-crt.inc.c
new file mode 100644
index XXXXXXX..XXXXXXX
--- /dev/null
+++ b/tests/tcg/aarch64/bti-crt.inc.c
@@ -XXX,XX +XXX,XX @@
+/*
+ * Minimal user-environment for testing BTI.
+ *
+ * Normal libc is not (yet) built with BTI support enabled,
+ * and so could generate a BTI TRAP before ever reaching main.
+ */
+
+#include <stdlib.h>
+#include <signal.h>
+#include <ucontext.h>
+#include <asm/unistd.h>
+
+int main(void);
+
+void _start(void)
+{
+    exit(main());
+}
+
+void exit(int ret)
+{
+    register int x0 __asm__("x0") = ret;
+    register int x8 __asm__("x8") = __NR_exit;
+
+    asm volatile("svc #0" : : "r"(x0), "r"(x8));
+    __builtin_unreachable();
+}
+
+/*
+ * Irritatingly, the user API struct sigaction does not match the
+ * kernel API struct sigaction.  So for simplicity, isolate the
+ * kernel ABI here, and make this act like signal.
+ */
+void signal_info(int sig, void (*fn)(int, siginfo_t *, ucontext_t *))
+{
+    struct kernel_sigaction {
+        void (*handler)(int, siginfo_t *, ucontext_t *);
+        unsigned long flags;
+        unsigned long restorer;
+        unsigned long mask;
+    } sa = { fn, SA_SIGINFO, 0, 0 };
+
+    register int x0 __asm__("x0") = sig;
+    register void *x1 __asm__("x1") = &sa;
+    register void *x2 __asm__("x2") = 0;
+    register int x3 __asm__("x3") = sizeof(unsigned long);
+    register int x8 __asm__("x8") = __NR_rt_sigaction;
+
+    asm volatile("svc #0"
+                 : : "r"(x0), "r"(x1), "r"(x2), "r"(x3), "r"(x8) : "memory");
+}
diff --git a/tests/tcg/aarch64/Makefile.target b/tests/tcg/aarch64/Makefile.target
index XXXXXXX..XXXXXXX 100644
--- a/tests/tcg/aarch64/Makefile.target
+++ b/tests/tcg/aarch64/Makefile.target
@@ -XXX,XX +XXX,XX @@ run-pauth-%: QEMU_OPTS += -cpu max
 pauth-%: CFLAGS += -march=armv8.3-a
 endif
 
+# BTI Tests
+ifneq ($(DOCKER_IMAGE)$(CROSS_CC_HAS_ARMV8_BTI),)
+AARCH64_TESTS += bti-1
+bti-%: CFLAGS += -mbranch-protection=standard
+bti-%: LDFLAGS += -nostdlib
+endif
+
 # Semihosting smoke test for linux-user
 AARCH64_TESTS += semihosting
 run-semihosting: semihosting
diff --git a/tests/tcg/configure.sh b/tests/tcg/configure.sh
index XXXXXXX..XXXXXXX 100755
--- a/tests/tcg/configure.sh
+++ b/tests/tcg/configure.sh
@@ -XXX,XX +XXX,XX @@ for target in $target_list; do
                -march=armv8.3-a -o $TMPE $TMPC; then
                 echo "CROSS_CC_HAS_ARMV8_3=y" >> $config_target_mak
             fi
+            if do_compiler "$target_compiler" $target_compiler_cflags \
+               -mbranch-protection=standard -o $TMPE $TMPC; then
+                echo "CROSS_CC_HAS_ARMV8_BTI=y" >> $config_target_mak
+            fi
         ;;
     esac
 
-- 
2.20.1

The kernel abi for this was merged in v5.8, just as the qemu 5.1
merge window was closing, so this slipped to the next dev cycle.

Changes from v9:
  * Split what is now patch 7 into 3 more (pmm).
  * All prerequisites are now upstream.

Richard Henderson (8):
  linux-user/aarch64: Reset btype for signals
  linux-user: Set PAGE_TARGET_1 for TARGET_PROT_BTI
  include/elf: Add defines related to GNU property notes for AArch64
  linux-user/elfload: Fix coding style in load_elf_image
  linux-user/elfload: Adjust iteration over phdr
  linux-user/elfload: Move PT_INTERP detection to first loop
  linux-user/elfload: Parse NT_GNU_PROPERTY_TYPE_0 notes
  tests/tcg/aarch64: Add bti smoke test

include/elf.h                     |  22 +++++
 include/exec/cpu-all.h            |   2 +
 linux-user/qemu.h                 |   4 +
 linux-user/syscall_defs.h         |   4 +
 target/arm/cpu.h                  |   5 +
 linux-user/aarch64/signal.c       |  10 +-
 linux-user/elfload.c              | 147 ++++++++++++++++++++++--------
 linux-user/mmap.c                 |  16 ++++
 target/arm/translate-a64.c        |   6 +-
 tests/tcg/aarch64/bti-1.c         |  62 +++++++++++++
 tests/tcg/aarch64/bti-crt.inc.c   |  51 +++++++++++
 tests/tcg/aarch64/Makefile.target |   7 ++
 tests/tcg/configure.sh            |   4 +
 13 files changed, 298 insertions(+), 42 deletions(-)
 create mode 100644 tests/tcg/aarch64/bti-1.c
 create mode 100644 tests/tcg/aarch64/bti-crt.inc.c

-- 
2.25.1

The kernel sets btype for the signal handler as if for a call.

Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
---
 linux-user/aarch64/signal.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

Transform the prot bit to a qemu internal page bit, and save
it in the page tables.

Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
---
v10: Add PAGE_BTI define (pmm).
---
 include/exec/cpu-all.h     |  2 ++
 linux-user/syscall_defs.h  |  4 ++++
 target/arm/cpu.h           |  5 +++++
 linux-user/mmap.c          | 16 ++++++++++++++++
 target/arm/translate-a64.c |  6 +++---
 5 files changed, 30 insertions(+), 3 deletions(-)

diff --git a/include/exec/cpu-all.h b/include/exec/cpu-all.h
index XXXXXXX..XXXXXXX 100644
--- a/include/exec/cpu-all.h
+++ b/include/exec/cpu-all.h
@@ -XXX,XX +XXX,XX @@ extern intptr_t qemu_host_page_mask;
 /* FIXME: Code that sets/uses this is broken and needs to go away.  */
 #define PAGE_RESERVED  0x0020
 #endif
+/* Target-specific bits that will be used via page_get_flags().  */
+#define PAGE_TARGET_1  0x0080
 
 #if defined(CONFIG_USER_ONLY)
 void page_dump(FILE *f);
diff --git a/linux-user/syscall_defs.h b/linux-user/syscall_defs.h
index XXXXXXX..XXXXXXX 100644
--- a/linux-user/syscall_defs.h
+++ b/linux-user/syscall_defs.h
@@ -XXX,XX +XXX,XX @@ struct target_winsize {
 #define TARGET_PROT_SEM         0x08
 #endif
 
+#ifdef TARGET_AARCH64
+#define TARGET_PROT_BTI         0x10
+#endif
+
 /* Common */
 #define TARGET_MAP_SHARED	0x01		/* Share changes */
 #define TARGET_MAP_PRIVATE	0x02		/* Changes are private */
diff --git a/target/arm/cpu.h b/target/arm/cpu.h
index XXXXXXX..XXXXXXX 100644
--- a/target/arm/cpu.h
+++ b/target/arm/cpu.h
@@ -XXX,XX +XXX,XX @@ static inline MemTxAttrs *typecheck_memtxattrs(MemTxAttrs *x)
 #define arm_tlb_bti_gp(x) (typecheck_memtxattrs(x)->target_tlb_bit0)
 #define arm_tlb_mte_tagged(x) (typecheck_memtxattrs(x)->target_tlb_bit1)
 
+/*
+ * AArch64 usage of the PAGE_TARGET_* bits for linux-user.
+ */
+#define PAGE_BTI  PAGE_TARGET_1
+
 /*
  * Naming convention for isar_feature functions:
  * Functions which test 32-bit ID registers should have _aa32_ in
diff --git a/linux-user/mmap.c b/linux-user/mmap.c
index XXXXXXX..XXXXXXX 100644
--- a/linux-user/mmap.c
+++ b/linux-user/mmap.c
@@ -XXX,XX +XXX,XX @@ static int validate_prot_to_pageflags(int *host_prot, int prot)
     *host_prot = (prot & (PROT_READ | PROT_WRITE))
                | (prot & PROT_EXEC ? PROT_READ : 0);
 
+#ifdef TARGET_AARCH64
+    /*
+     * The PROT_BTI bit is only accepted if the cpu supports the feature.
+     * Since this is the unusual case, don't bother checking unless
+     * the bit has been requested.  If set and valid, record the bit
+     * within QEMU's page_flags.
+     */
+    if (prot & TARGET_PROT_BTI) {
+        ARMCPU *cpu = ARM_CPU(thread_cpu);
+        if (cpu_isar_feature(aa64_bti, cpu)) {
+            valid |= TARGET_PROT_BTI;
+            page_flags |= PAGE_BTI;
+        }
+    }
+#endif
+
     return prot & ~valid ? 0 : page_flags;
 }
 
diff --git a/target/arm/translate-a64.c b/target/arm/translate-a64.c
index XXXXXXX..XXXXXXX 100644
--- a/target/arm/translate-a64.c
+++ b/target/arm/translate-a64.c
@@ -XXX,XX +XXX,XX @@ static void disas_data_proc_simd_fp(DisasContext *s, uint32_t insn)
  */
 static bool is_guarded_page(CPUARMState *env, DisasContext *s)
 {
-#ifdef CONFIG_USER_ONLY
-    return false;  /* FIXME */
-#else
     uint64_t addr = s->base.pc_first;
+#ifdef CONFIG_USER_ONLY
+    return page_get_flags(addr) & PAGE_BTI;
+#else
     int mmu_idx = arm_to_core_mmu_idx(s->mmu_idx);
     unsigned int index = tlb_index(env, mmu_idx, addr);
     CPUTLBEntry *entry = tlb_entry(env, mmu_idx, addr);
-- 
2.25.1

These are all of the defines required to parse
GNU_PROPERTY_AARCH64_FEATURE_1_AND, copied from binutils.
Other missing defines related to other GNU program headers
and notes are elided for now.

Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
---
 include/elf.h | 22 ++++++++++++++++++++++
 1 file changed, 22 insertions(+)

Fixing this now will clarify following patches.

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
---
 linux-user/elfload.c | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/linux-user/elfload.c b/linux-user/elfload.c
index XXXXXXX..XXXXXXX 100644
--- a/linux-user/elfload.c
+++ b/linux-user/elfload.c
@@ -XXX,XX +XXX,XX @@ static void load_elf_image(const char *image_name, int image_fd,
             abi_ulong vaddr, vaddr_po, vaddr_ps, vaddr_ef, vaddr_em, vaddr_len;
             int elf_prot = 0;
 
-            if (eppnt->p_flags & PF_R) elf_prot =  PROT_READ;
-            if (eppnt->p_flags & PF_W) elf_prot |= PROT_WRITE;
-            if (eppnt->p_flags & PF_X) elf_prot |= PROT_EXEC;
+            if (eppnt->p_flags & PF_R) {
+                elf_prot |= PROT_READ;
+            }
+            if (eppnt->p_flags & PF_W) {
+                elf_prot |= PROT_WRITE;
+            }
+            if (eppnt->p_flags & PF_X) {
+                elf_prot |= PROT_EXEC;
+            }
 
             vaddr = load_bias + eppnt->p_vaddr;
             vaddr_po = TARGET_ELF_PAGEOFFSET(vaddr);
-- 
2.25.1

The second loop uses a loop induction variable, and the first
does not.  Transform the first to match the second, to simplify
a following patch moving code between them.

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
---
 linux-user/elfload.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/linux-user/elfload.c b/linux-user/elfload.c
index XXXXXXX..XXXXXXX 100644
--- a/linux-user/elfload.c
+++ b/linux-user/elfload.c
@@ -XXX,XX +XXX,XX @@ static void load_elf_image(const char *image_name, int image_fd,
     loaddr = -1, hiaddr = 0;
     info->alignment = 0;
     for (i = 0; i < ehdr->e_phnum; ++i) {
-        if (phdr[i].p_type == PT_LOAD) {
-            abi_ulong a = phdr[i].p_vaddr - phdr[i].p_offset;
+        struct elf_phdr *eppnt = phdr + i;
+        if (eppnt->p_type == PT_LOAD) {
+            abi_ulong a = eppnt->p_vaddr - eppnt->p_offset;
             if (a < loaddr) {
                 loaddr = a;
             }
-            a = phdr[i].p_vaddr + phdr[i].p_memsz;
+            a = eppnt->p_vaddr + eppnt->p_memsz;
             if (a > hiaddr) {
                 hiaddr = a;
             }
             ++info->nsegs;
-            info->alignment |= phdr[i].p_align;
+            info->alignment |= eppnt->p_align;
         }
     }
 
-- 
2.25.1

For BTI, we need to know if the executable is static or dynamic,
which means looking for PT_INTERP earlier.

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
---
 linux-user/elfload.c | 60 +++++++++++++++++++++++---------------------
 1 file changed, 31 insertions(+), 29 deletions(-)

diff --git a/linux-user/elfload.c b/linux-user/elfload.c
index XXXXXXX..XXXXXXX 100644
--- a/linux-user/elfload.c
+++ b/linux-user/elfload.c
@@ -XXX,XX +XXX,XX @@ static void load_elf_image(const char *image_name, int image_fd,
 
     mmap_lock();
 
-    /* Find the maximum size of the image and allocate an appropriate
-       amount of memory to handle that.  */
+    /*
+     * Find the maximum size of the image and allocate an appropriate
+     * amount of memory to handle that.  Locate the interpreter, if any.
+     */
     loaddr = -1, hiaddr = 0;
     info->alignment = 0;
     for (i = 0; i < ehdr->e_phnum; ++i) {
@@ -XXX,XX +XXX,XX @@ static void load_elf_image(const char *image_name, int image_fd,
             }
             ++info->nsegs;
             info->alignment |= eppnt->p_align;
+        } else if (eppnt->p_type == PT_INTERP && pinterp_name) {
+            char *interp_name;
+
+            if (*pinterp_name) {
+                errmsg = "Multiple PT_INTERP entries";
+                goto exit_errmsg;
+            }
+            interp_name = malloc(eppnt->p_filesz);
+            if (!interp_name) {
+                goto exit_perror;
+            }
+
+            if (eppnt->p_offset + eppnt->p_filesz <= BPRM_BUF_SIZE) {
+                memcpy(interp_name, bprm_buf + eppnt->p_offset,
+                       eppnt->p_filesz);
+            } else {
+                retval = pread(image_fd, interp_name, eppnt->p_filesz,
+                               eppnt->p_offset);
+                if (retval != eppnt->p_filesz) {
+                    goto exit_perror;
+                }
+            }
+            if (interp_name[eppnt->p_filesz - 1] != 0) {
+                errmsg = "Invalid PT_INTERP entry";
+                goto exit_errmsg;
+            }
+            *pinterp_name = interp_name;
         }
     }
 
@@ -XXX,XX +XXX,XX @@ static void load_elf_image(const char *image_name, int image_fd,
             if (vaddr_em > info->brk) {
                 info->brk = vaddr_em;
             }
-        } else if (eppnt->p_type == PT_INTERP && pinterp_name) {
-            char *interp_name;
-
-            if (*pinterp_name) {
-                errmsg = "Multiple PT_INTERP entries";
-                goto exit_errmsg;
-            }
-            interp_name = malloc(eppnt->p_filesz);
-            if (!interp_name) {
-                goto exit_perror;
-            }
-
-            if (eppnt->p_offset + eppnt->p_filesz <= BPRM_BUF_SIZE) {
-                memcpy(interp_name, bprm_buf + eppnt->p_offset,
-                       eppnt->p_filesz);
-            } else {
-                retval = pread(image_fd, interp_name, eppnt->p_filesz,
-                               eppnt->p_offset);
-                if (retval != eppnt->p_filesz) {
-                    goto exit_perror;
-                }
-            }
-            if (interp_name[eppnt->p_filesz - 1] != 0) {
-                errmsg = "Invalid PT_INTERP entry";
-                goto exit_errmsg;
-            }
-            *pinterp_name = interp_name;
 #ifdef TARGET_MIPS
         } else if (eppnt->p_type == PT_MIPS_ABIFLAGS) {
             Mips_elf_abiflags_v0 abiflags;
-- 
2.25.1

For aarch64, this includes the GNU_PROPERTY_AARCH64_FEATURE_1_BTI bit,
which indicates that the image should be mapped with guarded pages.

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
---
v9: Only map the startup executable with BTI; anything else must be
    handled by the interpreter.
v10: Split out preparatory patches (pmm).
---
 linux-user/qemu.h    |  4 +++
 linux-user/elfload.c | 68 ++++++++++++++++++++++++++++++++++++++++++--
 2 files changed, 70 insertions(+), 2 deletions(-)

This test requires gcc 10 for -mbranch-protection=standard.

Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
---
v9: Expect and require gcc 10.
---
 tests/tcg/aarch64/bti-1.c         | 62 +++++++++++++++++++++++++++++++
 tests/tcg/aarch64/bti-crt.inc.c   | 51 +++++++++++++++++++++++++
 tests/tcg/aarch64/Makefile.target |  7 ++++
 tests/tcg/configure.sh            |  4 ++
 4 files changed, 124 insertions(+)
 create mode 100644 tests/tcg/aarch64/bti-1.c
 create mode 100644 tests/tcg/aarch64/bti-crt.inc.c

diff --git a/tests/tcg/aarch64/bti-1.c b/tests/tcg/aarch64/bti-1.c
new file mode 100644
index XXXXXXX..XXXXXXX
--- /dev/null
+++ b/tests/tcg/aarch64/bti-1.c
@@ -XXX,XX +XXX,XX @@
+/*
+ * Branch target identification, basic notskip cases.
+ */
+
+#include "bti-crt.inc.c"
+
+static void skip2_sigill(int sig, siginfo_t *info, ucontext_t *uc)
+{
+    uc->uc_mcontext.pc += 8;
+    uc->uc_mcontext.pstate = 1;
+}
+
+#define NOP       "nop"
+#define BTI_N     "hint #32"
+#define BTI_C     "hint #34"
+#define BTI_J     "hint #36"
+#define BTI_JC    "hint #38"
+
+#define BTYPE_1(DEST) \
+    asm("mov %0,#1; adr x16, 1f; br x16; 1: " DEST "; mov %0,#0" \
+        : "=r"(skipped) : : "x16")
+
+#define BTYPE_2(DEST) \
+    asm("mov %0,#1; adr x16, 1f; blr x16; 1: " DEST "; mov %0,#0" \
+        : "=r"(skipped) : : "x16", "x30")
+
+#define BTYPE_3(DEST) \
+    asm("mov %0,#1; adr x15, 1f; br x15; 1: " DEST "; mov %0,#0" \
+        : "=r"(skipped) : : "x15")
+
+#define TEST(WHICH, DEST, EXPECT) \
+    do { WHICH(DEST); fail += skipped ^ EXPECT; } while (0)
+
+
+int main()
+{
+    int fail = 0;
+    int skipped;
+
+    /* Signal-like with SA_SIGINFO.  */
+    signal_info(SIGILL, skip2_sigill);
+
+    TEST(BTYPE_1, NOP, 1);
+    TEST(BTYPE_1, BTI_N, 1);
+    TEST(BTYPE_1, BTI_C, 0);
+    TEST(BTYPE_1, BTI_J, 0);
+    TEST(BTYPE_1, BTI_JC, 0);
+
+    TEST(BTYPE_2, NOP, 1);
+    TEST(BTYPE_2, BTI_N, 1);
+    TEST(BTYPE_2, BTI_C, 0);
+    TEST(BTYPE_2, BTI_J, 1);
+    TEST(BTYPE_2, BTI_JC, 0);
+
+    TEST(BTYPE_3, NOP, 1);
+    TEST(BTYPE_3, BTI_N, 1);
+    TEST(BTYPE_3, BTI_C, 1);
+    TEST(BTYPE_3, BTI_J, 0);
+    TEST(BTYPE_3, BTI_JC, 0);
+
+    return fail;
+}
diff --git a/tests/tcg/aarch64/bti-crt.inc.c b/tests/tcg/aarch64/bti-crt.inc.c
new file mode 100644
index XXXXXXX..XXXXXXX
--- /dev/null
+++ b/tests/tcg/aarch64/bti-crt.inc.c
@@ -XXX,XX +XXX,XX @@
+/*
+ * Minimal user-environment for testing BTI.
+ *
+ * Normal libc is not (yet) built with BTI support enabled,
+ * and so could generate a BTI TRAP before ever reaching main.
+ */
+
+#include <stdlib.h>
+#include <signal.h>
+#include <ucontext.h>
+#include <asm/unistd.h>
+
+int main(void);
+
+void _start(void)
+{
+    exit(main());
+}
+
+void exit(int ret)
+{
+    register int x0 __asm__("x0") = ret;
+    register int x8 __asm__("x8") = __NR_exit;
+
+    asm volatile("svc #0" : : "r"(x0), "r"(x8));
+    __builtin_unreachable();
+}
+
+/*
+ * Irritatingly, the user API struct sigaction does not match the
+ * kernel API struct sigaction.  So for simplicity, isolate the
+ * kernel ABI here, and make this act like signal.
+ */
+void signal_info(int sig, void (*fn)(int, siginfo_t *, ucontext_t *))
+{
+    struct kernel_sigaction {
+        void (*handler)(int, siginfo_t *, ucontext_t *);
+        unsigned long flags;
+        unsigned long restorer;
+        unsigned long mask;
+    } sa = { fn, SA_SIGINFO, 0, 0 };
+
+    register int x0 __asm__("x0") = sig;
+    register void *x1 __asm__("x1") = &sa;
+    register void *x2 __asm__("x2") = 0;
+    register int x3 __asm__("x3") = sizeof(unsigned long);
+    register int x8 __asm__("x8") = __NR_rt_sigaction;
+
+    asm volatile("svc #0"
+                 : : "r"(x0), "r"(x1), "r"(x2), "r"(x3), "r"(x8) : "memory");
+}
diff --git a/tests/tcg/aarch64/Makefile.target b/tests/tcg/aarch64/Makefile.target
index XXXXXXX..XXXXXXX 100644
--- a/tests/tcg/aarch64/Makefile.target
+++ b/tests/tcg/aarch64/Makefile.target
@@ -XXX,XX +XXX,XX @@ run-pauth-%: QEMU_OPTS += -cpu max
 run-plugin-pauth-%: QEMU_OPTS += -cpu max
 endif
 
+# BTI Tests
+ifneq ($(DOCKER_IMAGE)$(CROSS_CC_HAS_ARMV8_BTI),)
+AARCH64_TESTS += bti-1
+bti-%: CFLAGS += -mbranch-protection=standard
+bti-%: LDFLAGS += -nostdlib
+endif
+
 # Semihosting smoke test for linux-user
 AARCH64_TESTS += semihosting
 run-semihosting: semihosting
diff --git a/tests/tcg/configure.sh b/tests/tcg/configure.sh
index XXXXXXX..XXXXXXX 100755
--- a/tests/tcg/configure.sh
+++ b/tests/tcg/configure.sh
@@ -XXX,XX +XXX,XX @@ for target in $target_list; do
                -march=armv8.3-a -o $TMPE $TMPC; then
                 echo "CROSS_CC_HAS_ARMV8_3=y" >> $config_target_mak
             fi
+            if do_compiler "$target_compiler" $target_compiler_cflags \
+               -mbranch-protection=standard -o $TMPE $TMPC; then
+                echo "CROSS_CC_HAS_ARMV8_BTI=y" >> $config_target_mak
+            fi
         ;;
     esac
 
-- 
2.25.1