From: Ard Biesheuvel <ardb@kernel.org>
Move the early GDT/IDT setup code that runs long before the kernel
virtual mapping is up into arch/x86/boot/startup/, and build it in a way
that ensures that the code tolerates being called from the 1:1 mapping
of memory. The code itself is left unchanged by this patch.
Also tweak the sed symbol matching pattern in the decompressor to match
on lower case 't' or 'b', as these will be emitted by Clang for symbols
with hidden linkage.
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
---
arch/x86/boot/compressed/Makefile | 2 +-
arch/x86/boot/startup/Makefile | 15 ++++
arch/x86/boot/startup/gdt_idt.c | 83 ++++++++++++++++++++
arch/x86/kernel/head64.c | 73 -----------------
4 files changed, 99 insertions(+), 74 deletions(-)
diff --git a/arch/x86/boot/compressed/Makefile b/arch/x86/boot/compressed/Makefile
index 37b85ce9b2a3..0fcad7b7e007 100644
--- a/arch/x86/boot/compressed/Makefile
+++ b/arch/x86/boot/compressed/Makefile
@@ -73,7 +73,7 @@ LDFLAGS_vmlinux += -T
hostprogs := mkpiggy
HOST_EXTRACFLAGS += -I$(srctree)/tools/include
-sed-voffset := -e 's/^\([0-9a-fA-F]*\) [ABCDGRSTVW] \(_text\|__start_rodata\|__bss_start\|_end\)$$/\#define VO_\2 _AC(0x\1,UL)/p'
+sed-voffset := -e 's/^\([0-9a-fA-F]*\) [ABbCDGRSTtVW] \(_text\|__start_rodata\|__bss_start\|_end\)$$/\#define VO_\2 _AC(0x\1,UL)/p'
quiet_cmd_voffset = VOFFSET $@
cmd_voffset = $(NM) $< | sed -n $(sed-voffset) > $@
diff --git a/arch/x86/boot/startup/Makefile b/arch/x86/boot/startup/Makefile
index 8919a1cbcb5a..1beb5de30735 100644
--- a/arch/x86/boot/startup/Makefile
+++ b/arch/x86/boot/startup/Makefile
@@ -1,6 +1,21 @@
# SPDX-License-Identifier: GPL-2.0
KBUILD_AFLAGS += -D__DISABLE_EXPORTS
+KBUILD_CFLAGS += -D__DISABLE_EXPORTS -mcmodel=small -fPIC \
+ -Os -DDISABLE_BRANCH_PROFILING \
+ $(DISABLE_STACKLEAK_PLUGIN) \
+ -fno-stack-protector -D__NO_FORTIFY \
+ -include $(srctree)/include/linux/hidden.h
+
+# disable ftrace hooks
+KBUILD_CFLAGS := $(subst $(CC_FLAGS_FTRACE),,$(KBUILD_CFLAGS))
+KASAN_SANITIZE := n
+KCSAN_SANITIZE := n
+KMSAN_SANITIZE := n
+UBSAN_SANITIZE := n
+KCOV_INSTRUMENT := n
+
+obj-$(CONFIG_X86_64) += gdt_idt.o
lib-$(CONFIG_X86_64) += la57toggle.o
lib-$(CONFIG_EFI_MIXED) += efi-mixed.o
diff --git a/arch/x86/boot/startup/gdt_idt.c b/arch/x86/boot/startup/gdt_idt.c
new file mode 100644
index 000000000000..1ba6bd5786fe
--- /dev/null
+++ b/arch/x86/boot/startup/gdt_idt.c
@@ -0,0 +1,83 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/linkage.h>
+#include <linux/types.h>
+
+#include <asm/desc.h>
+#include <asm/init.h>
+#include <asm/setup.h>
+#include <asm/sev.h>
+#include <asm/trapnr.h>
+
+/*
+ * Data structures and code used for IDT setup in head_64.S. The bringup-IDT is
+ * used until the idt_table takes over. On the boot CPU this happens in
+ * x86_64_start_kernel(), on secondary CPUs in start_secondary(). In both cases
+ * this happens in the functions called from head_64.S.
+ *
+ * The idt_table can't be used that early because all the code modifying it is
+ * in idt.c and can be instrumented by tracing or KASAN, which both don't work
+ * during early CPU bringup. Also the idt_table has the runtime vectors
+ * configured which require certain CPU state to be setup already (like TSS),
+ * which also hasn't happened yet in early CPU bringup.
+ */
+static gate_desc bringup_idt_table[NUM_EXCEPTION_VECTORS] __page_aligned_data;
+
+/* This may run while still in the direct mapping */
+static void __head startup_64_load_idt(void *vc_handler)
+{
+ struct desc_ptr desc = {
+ .address = (unsigned long)rip_rel_ptr(bringup_idt_table),
+ .size = sizeof(bringup_idt_table) - 1,
+ };
+ struct idt_data data;
+ gate_desc idt_desc;
+
+ /* @vc_handler is set only for a VMM Communication Exception */
+ if (vc_handler) {
+ init_idt_data(&data, X86_TRAP_VC, vc_handler);
+ idt_init_desc(&idt_desc, &data);
+ native_write_idt_entry((gate_desc *)desc.address, X86_TRAP_VC, &idt_desc);
+ }
+
+ native_load_idt(&desc);
+}
+
+/* This is used when running on kernel addresses */
+void early_setup_idt(void)
+{
+ void *handler = NULL;
+
+ if (IS_ENABLED(CONFIG_AMD_MEM_ENCRYPT)) {
+ setup_ghcb();
+ handler = vc_boot_ghcb;
+ }
+
+ startup_64_load_idt(handler);
+}
+
+/*
+ * Setup boot CPU state needed before kernel switches to virtual addresses.
+ */
+void __head startup_64_setup_gdt_idt(void)
+{
+ void *handler = NULL;
+
+ struct desc_ptr startup_gdt_descr = {
+ .address = (unsigned long)rip_rel_ptr((__force void *)&gdt_page),
+ .size = GDT_SIZE - 1,
+ };
+
+ /* Load GDT */
+ native_load_gdt(&startup_gdt_descr);
+
+ /* New GDT is live - reload data segment registers */
+ asm volatile("movl %%eax, %%ds\n"
+ "movl %%eax, %%ss\n"
+ "movl %%eax, %%es\n" : : "a"(__KERNEL_DS) : "memory");
+
+ if (IS_ENABLED(CONFIG_AMD_MEM_ENCRYPT))
+ handler = rip_rel_ptr(vc_no_ghcb);
+
+ startup_64_load_idt(handler);
+}
diff --git a/arch/x86/kernel/head64.c b/arch/x86/kernel/head64.c
index 3fb23d805cef..9b2ffec4bbad 100644
--- a/arch/x86/kernel/head64.c
+++ b/arch/x86/kernel/head64.c
@@ -512,76 +512,3 @@ void __init __noreturn x86_64_start_reservations(char *real_mode_data)
start_kernel();
}
-
-/*
- * Data structures and code used for IDT setup in head_64.S. The bringup-IDT is
- * used until the idt_table takes over. On the boot CPU this happens in
- * x86_64_start_kernel(), on secondary CPUs in start_secondary(). In both cases
- * this happens in the functions called from head_64.S.
- *
- * The idt_table can't be used that early because all the code modifying it is
- * in idt.c and can be instrumented by tracing or KASAN, which both don't work
- * during early CPU bringup. Also the idt_table has the runtime vectors
- * configured which require certain CPU state to be setup already (like TSS),
- * which also hasn't happened yet in early CPU bringup.
- */
-static gate_desc bringup_idt_table[NUM_EXCEPTION_VECTORS] __page_aligned_data;
-
-/* This may run while still in the direct mapping */
-static void __head startup_64_load_idt(void *vc_handler)
-{
- struct desc_ptr desc = {
- .address = (unsigned long)rip_rel_ptr(bringup_idt_table),
- .size = sizeof(bringup_idt_table) - 1,
- };
- struct idt_data data;
- gate_desc idt_desc;
-
- /* @vc_handler is set only for a VMM Communication Exception */
- if (vc_handler) {
- init_idt_data(&data, X86_TRAP_VC, vc_handler);
- idt_init_desc(&idt_desc, &data);
- native_write_idt_entry((gate_desc *)desc.address, X86_TRAP_VC, &idt_desc);
- }
-
- native_load_idt(&desc);
-}
-
-/* This is used when running on kernel addresses */
-void early_setup_idt(void)
-{
- void *handler = NULL;
-
- if (IS_ENABLED(CONFIG_AMD_MEM_ENCRYPT)) {
- setup_ghcb();
- handler = vc_boot_ghcb;
- }
-
- startup_64_load_idt(handler);
-}
-
-/*
- * Setup boot CPU state needed before kernel switches to virtual addresses.
- */
-void __head startup_64_setup_gdt_idt(void)
-{
- void *handler = NULL;
-
- struct desc_ptr startup_gdt_descr = {
- .address = (unsigned long)rip_rel_ptr((__force void *)&gdt_page),
- .size = GDT_SIZE - 1,
- };
-
- /* Load GDT */
- native_load_gdt(&startup_gdt_descr);
-
- /* New GDT is live - reload data segment registers */
- asm volatile("movl %%eax, %%ds\n"
- "movl %%eax, %%ss\n"
- "movl %%eax, %%es\n" : : "a"(__KERNEL_DS) : "memory");
-
- if (IS_ENABLED(CONFIG_AMD_MEM_ENCRYPT))
- handler = rip_rel_ptr(vc_no_ghcb);
-
- startup_64_load_idt(handler);
-}
--
2.49.0.504.g3bcea36a83-goog* Ard Biesheuvel <ardb+git@google.com> wrote: > From: Ard Biesheuvel <ardb@kernel.org> > > Move the early GDT/IDT setup code that runs long before the kernel > virtual mapping is up into arch/x86/boot/startup/, and build it in a way > that ensures that the code tolerates being called from the 1:1 mapping > of memory. The code itself is left unchanged by this patch. > > Also tweak the sed symbol matching pattern in the decompressor to match > on lower case 't' or 'b', as these will be emitted by Clang for symbols > with hidden linkage. > > Signed-off-by: Ard Biesheuvel <ardb@kernel.org> > --- > arch/x86/boot/compressed/Makefile | 2 +- > arch/x86/boot/startup/Makefile | 15 ++++ > arch/x86/boot/startup/gdt_idt.c | 83 ++++++++++++++++++++ > arch/x86/kernel/head64.c | 73 ----------------- > 4 files changed, 99 insertions(+), 74 deletions(-) This causes the following build failure on x86-64-defconfig: arch/x86/boot/startup/gdt_idt.c:67:55: error: cast to generic address space pointer from disjoint ‘__seg_gs’ address space pointer [-Werror] Thanks, Ingo
* Ingo Molnar <mingo@kernel.org> wrote: > > * Ard Biesheuvel <ardb+git@google.com> wrote: > > > From: Ard Biesheuvel <ardb@kernel.org> > > > > Move the early GDT/IDT setup code that runs long before the kernel > > virtual mapping is up into arch/x86/boot/startup/, and build it in a way > > that ensures that the code tolerates being called from the 1:1 mapping > > of memory. The code itself is left unchanged by this patch. > > > > Also tweak the sed symbol matching pattern in the decompressor to match > > on lower case 't' or 'b', as these will be emitted by Clang for symbols > > with hidden linkage. > > > > Signed-off-by: Ard Biesheuvel <ardb@kernel.org> > > --- > > arch/x86/boot/compressed/Makefile | 2 +- > > arch/x86/boot/startup/Makefile | 15 ++++ > > arch/x86/boot/startup/gdt_idt.c | 83 ++++++++++++++++++++ > > arch/x86/kernel/head64.c | 73 ----------------- > > 4 files changed, 99 insertions(+), 74 deletions(-) > > This causes the following build failure on x86-64-defconfig: > > arch/x86/boot/startup/gdt_idt.c:67:55: error: cast to generic address space pointer from disjoint ‘__seg_gs’ address space pointer [-Werror] Caused by the previous patch: x86/asm: Make rip_rel_ptr() usable from fPIC code Thanks, Ingo
On Wed, 9 Apr 2025 at 12:07, Ingo Molnar <mingo@kernel.org> wrote: > > > * Ingo Molnar <mingo@kernel.org> wrote: > > > > > * Ard Biesheuvel <ardb+git@google.com> wrote: > > > > > From: Ard Biesheuvel <ardb@kernel.org> > > > > > > Move the early GDT/IDT setup code that runs long before the kernel > > > virtual mapping is up into arch/x86/boot/startup/, and build it in a way > > > that ensures that the code tolerates being called from the 1:1 mapping > > > of memory. The code itself is left unchanged by this patch. > > > > > > Also tweak the sed symbol matching pattern in the decompressor to match > > > on lower case 't' or 'b', as these will be emitted by Clang for symbols > > > with hidden linkage. > > > > > > Signed-off-by: Ard Biesheuvel <ardb@kernel.org> > > > --- > > > arch/x86/boot/compressed/Makefile | 2 +- > > > arch/x86/boot/startup/Makefile | 15 ++++ > > > arch/x86/boot/startup/gdt_idt.c | 83 ++++++++++++++++++++ > > > arch/x86/kernel/head64.c | 73 ----------------- > > > 4 files changed, 99 insertions(+), 74 deletions(-) > > > > This causes the following build failure on x86-64-defconfig: > > > > arch/x86/boot/startup/gdt_idt.c:67:55: error: cast to generic address space pointer from disjoint ‘__seg_gs’ address space pointer [-Werror] > > Caused by the previous patch: > > x86/asm: Make rip_rel_ptr() usable from fPIC code > Oops, sorry about that. I saw that error and thought I had fixed it with the (__force void*) cast.
* Ard Biesheuvel <ardb@kernel.org> wrote: > On Wed, 9 Apr 2025 at 12:07, Ingo Molnar <mingo@kernel.org> wrote: > > > > > > * Ingo Molnar <mingo@kernel.org> wrote: > > > > > > > > * Ard Biesheuvel <ardb+git@google.com> wrote: > > > > > > > From: Ard Biesheuvel <ardb@kernel.org> > > > > > > > > Move the early GDT/IDT setup code that runs long before the kernel > > > > virtual mapping is up into arch/x86/boot/startup/, and build it in a way > > > > that ensures that the code tolerates being called from the 1:1 mapping > > > > of memory. The code itself is left unchanged by this patch. > > > > > > > > Also tweak the sed symbol matching pattern in the decompressor to match > > > > on lower case 't' or 'b', as these will be emitted by Clang for symbols > > > > with hidden linkage. > > > > > > > > Signed-off-by: Ard Biesheuvel <ardb@kernel.org> > > > > --- > > > > arch/x86/boot/compressed/Makefile | 2 +- > > > > arch/x86/boot/startup/Makefile | 15 ++++ > > > > arch/x86/boot/startup/gdt_idt.c | 83 ++++++++++++++++++++ > > > > arch/x86/kernel/head64.c | 73 ----------------- > > > > 4 files changed, 99 insertions(+), 74 deletions(-) > > > > > > This causes the following build failure on x86-64-defconfig: > > > > > > arch/x86/boot/startup/gdt_idt.c:67:55: error: cast to generic address space pointer from disjoint ‘__seg_gs’ address space pointer [-Werror] > > > > Caused by the previous patch: > > > > x86/asm: Make rip_rel_ptr() usable from fPIC code > > > > Oops, sorry about that. I saw that error and thought I had fixed it > with the (__force void*) cast. NP, caught it early enough. Thanks, Ingo
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