The direct-call syscall dispatch function doesn't know that the exit()
and exit_group() syscall handlers don't return, so the call sites aren't
optimized accordingly.
Fix that by marking the exit syscall declarations __noreturn.
Fixes the following warnings:
vmlinux.o: warning: objtool: x64_sys_call+0x2804: __x64_sys_exit() is missing a __noreturn annotation
vmlinux.o: warning: objtool: ia32_sys_call+0x29b6: __ia32_sys_exit_group() is missing a __noreturn annotation
Fixes: 7390db8aea0d ("x86/bhi: Add support for clearing branch history at syscall entry")
Reported-by: "Paul E. McKenney" <paulmck@kernel.org>
Closes: https://lkml.kernel.org/lkml/6dba9b32-db2c-4e6d-9500-7a08852f17a3@paulmck-laptop
Tested-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
---
arch/x86/entry/syscall_32.c | 10 ++++++----
arch/x86/entry/syscall_64.c | 9 ++++++---
arch/x86/entry/syscall_x32.c | 7 +++++--
arch/x86/entry/syscalls/syscall_32.tbl | 6 +++---
arch/x86/entry/syscalls/syscall_64.tbl | 6 +++---
arch/x86/um/sys_call_table_32.c | 10 ++++++----
arch/x86/um/sys_call_table_64.c | 11 +++++++----
scripts/syscalltbl.sh | 18 ++++++++++++++++--
tools/objtool/noreturns.h | 4 ++++
9 files changed, 56 insertions(+), 25 deletions(-)
diff --git a/arch/x86/entry/syscall_32.c b/arch/x86/entry/syscall_32.c
index c2235bae17ef..8cc9950d7104 100644
--- a/arch/x86/entry/syscall_32.c
+++ b/arch/x86/entry/syscall_32.c
@@ -14,9 +14,12 @@
#endif
#define __SYSCALL(nr, sym) extern long __ia32_##sym(const struct pt_regs *);
-
+#define __SYSCALL_NORETURN(nr, sym) extern long __noreturn __ia32_##sym(const struct pt_regs *);
#include <asm/syscalls_32.h>
-#undef __SYSCALL
+#undef __SYSCALL
+
+#undef __SYSCALL_NORETURN
+#define __SYSCALL_NORETURN __SYSCALL
/*
* The sys_call_table[] is no longer used for system calls, but
@@ -28,11 +31,10 @@
const sys_call_ptr_t sys_call_table[] = {
#include <asm/syscalls_32.h>
};
-#undef __SYSCALL
+#undef __SYSCALL
#endif
#define __SYSCALL(nr, sym) case nr: return __ia32_##sym(regs);
-
long ia32_sys_call(const struct pt_regs *regs, unsigned int nr)
{
switch (nr) {
diff --git a/arch/x86/entry/syscall_64.c b/arch/x86/entry/syscall_64.c
index 33b3f09e6f15..ba8354424860 100644
--- a/arch/x86/entry/syscall_64.c
+++ b/arch/x86/entry/syscall_64.c
@@ -8,8 +8,12 @@
#include <asm/syscall.h>
#define __SYSCALL(nr, sym) extern long __x64_##sym(const struct pt_regs *);
+#define __SYSCALL_NORETURN(nr, sym) extern long __noreturn __x64_##sym(const struct pt_regs *);
#include <asm/syscalls_64.h>
-#undef __SYSCALL
+#undef __SYSCALL
+
+#undef __SYSCALL_NORETURN
+#define __SYSCALL_NORETURN __SYSCALL
/*
* The sys_call_table[] is no longer used for system calls, but
@@ -20,10 +24,9 @@
const sys_call_ptr_t sys_call_table[] = {
#include <asm/syscalls_64.h>
};
-#undef __SYSCALL
+#undef __SYSCALL
#define __SYSCALL(nr, sym) case nr: return __x64_##sym(regs);
-
long x64_sys_call(const struct pt_regs *regs, unsigned int nr)
{
switch (nr) {
diff --git a/arch/x86/entry/syscall_x32.c b/arch/x86/entry/syscall_x32.c
index 03de4a932131..fb77908f44f3 100644
--- a/arch/x86/entry/syscall_x32.c
+++ b/arch/x86/entry/syscall_x32.c
@@ -8,11 +8,14 @@
#include <asm/syscall.h>
#define __SYSCALL(nr, sym) extern long __x64_##sym(const struct pt_regs *);
+#define __SYSCALL_NORETURN(nr, sym) extern long __noreturn __x64_##sym(const struct pt_regs *);
#include <asm/syscalls_x32.h>
-#undef __SYSCALL
+#undef __SYSCALL
+
+#undef __SYSCALL_NORETURN
+#define __SYSCALL_NORETURN __SYSCALL
#define __SYSCALL(nr, sym) case nr: return __x64_##sym(regs);
-
long x32_sys_call(const struct pt_regs *regs, unsigned int nr)
{
switch (nr) {
diff --git a/arch/x86/entry/syscalls/syscall_32.tbl b/arch/x86/entry/syscalls/syscall_32.tbl
index 7fd1f57ad3d3..09ca75bb51a0 100644
--- a/arch/x86/entry/syscalls/syscall_32.tbl
+++ b/arch/x86/entry/syscalls/syscall_32.tbl
@@ -2,7 +2,7 @@
# 32-bit system call numbers and entry vectors
#
# The format is:
-# <number> <abi> <name> <entry point> <compat entry point>
+# <number> <abi> <name> <entry point> [<compat entry point> [noreturn]]
#
# The __ia32_sys and __ia32_compat_sys stubs are created on-the-fly for
# sys_*() system calls and compat_sys_*() compat system calls if
@@ -12,7 +12,7 @@
# The abi is always "i386" for this file.
#
0 i386 restart_syscall sys_restart_syscall
-1 i386 exit sys_exit
+1 i386 exit sys_exit - noreturn
2 i386 fork sys_fork
3 i386 read sys_read
4 i386 write sys_write
@@ -263,7 +263,7 @@
249 i386 io_cancel sys_io_cancel
250 i386 fadvise64 sys_ia32_fadvise64
# 251 is available for reuse (was briefly sys_set_zone_reclaim)
-252 i386 exit_group sys_exit_group
+252 i386 exit_group sys_exit_group - noreturn
253 i386 lookup_dcookie
254 i386 epoll_create sys_epoll_create
255 i386 epoll_ctl sys_epoll_ctl
diff --git a/arch/x86/entry/syscalls/syscall_64.tbl b/arch/x86/entry/syscalls/syscall_64.tbl
index a396f6e6ab5b..a8068f937290 100644
--- a/arch/x86/entry/syscalls/syscall_64.tbl
+++ b/arch/x86/entry/syscalls/syscall_64.tbl
@@ -2,7 +2,7 @@
# 64-bit system call numbers and entry vectors
#
# The format is:
-# <number> <abi> <name> <entry point>
+# <number> <abi> <name> <entry point> [<compat entry point> [noreturn]]
#
# The __x64_sys_*() stubs are created on-the-fly for sys_*() system calls
#
@@ -68,7 +68,7 @@
57 common fork sys_fork
58 common vfork sys_vfork
59 64 execve sys_execve
-60 common exit sys_exit
+60 common exit sys_exit - noreturn
61 common wait4 sys_wait4
62 common kill sys_kill
63 common uname sys_newuname
@@ -239,7 +239,7 @@
228 common clock_gettime sys_clock_gettime
229 common clock_getres sys_clock_getres
230 common clock_nanosleep sys_clock_nanosleep
-231 common exit_group sys_exit_group
+231 common exit_group sys_exit_group - noreturn
232 common epoll_wait sys_epoll_wait
233 common epoll_ctl sys_epoll_ctl
234 common tgkill sys_tgkill
diff --git a/arch/x86/um/sys_call_table_32.c b/arch/x86/um/sys_call_table_32.c
index 89df5d89d664..51655133eee3 100644
--- a/arch/x86/um/sys_call_table_32.c
+++ b/arch/x86/um/sys_call_table_32.c
@@ -9,6 +9,10 @@
#include <linux/cache.h>
#include <asm/syscall.h>
+extern asmlinkage long sys_ni_syscall(unsigned long, unsigned long,
+ unsigned long, unsigned long,
+ unsigned long, unsigned long);
+
/*
* Below you can see, in terms of #define's, the differences between the x86-64
* and the UML syscall table.
@@ -22,15 +26,13 @@
#define sys_vm86 sys_ni_syscall
#define __SYSCALL_WITH_COMPAT(nr, native, compat) __SYSCALL(nr, native)
+#define __SYSCALL_NORETURN __SYSCALL
#define __SYSCALL(nr, sym) extern asmlinkage long sym(unsigned long, unsigned long, unsigned long, unsigned long, unsigned long, unsigned long);
#include <asm/syscalls_32.h>
+#undef __SYSCALL
-#undef __SYSCALL
#define __SYSCALL(nr, sym) sym,
-
-extern asmlinkage long sys_ni_syscall(unsigned long, unsigned long, unsigned long, unsigned long, unsigned long, unsigned long);
-
const sys_call_ptr_t sys_call_table[] ____cacheline_aligned = {
#include <asm/syscalls_32.h>
};
diff --git a/arch/x86/um/sys_call_table_64.c b/arch/x86/um/sys_call_table_64.c
index b0b4cfd2308c..943d414f2109 100644
--- a/arch/x86/um/sys_call_table_64.c
+++ b/arch/x86/um/sys_call_table_64.c
@@ -9,6 +9,10 @@
#include <linux/cache.h>
#include <asm/syscall.h>
+extern asmlinkage long sys_ni_syscall(unsigned long, unsigned long,
+ unsigned long, unsigned long,
+ unsigned long, unsigned long);
+
/*
* Below you can see, in terms of #define's, the differences between the x86-64
* and the UML syscall table.
@@ -18,14 +22,13 @@
#define sys_iopl sys_ni_syscall
#define sys_ioperm sys_ni_syscall
+#define __SYSCALL_NORETURN __SYSCALL
+
#define __SYSCALL(nr, sym) extern asmlinkage long sym(unsigned long, unsigned long, unsigned long, unsigned long, unsigned long, unsigned long);
#include <asm/syscalls_64.h>
+#undef __SYSCALL
-#undef __SYSCALL
#define __SYSCALL(nr, sym) sym,
-
-extern asmlinkage long sys_ni_syscall(unsigned long, unsigned long, unsigned long, unsigned long, unsigned long, unsigned long);
-
const sys_call_ptr_t sys_call_table[] ____cacheline_aligned = {
#include <asm/syscalls_64.h>
};
diff --git a/scripts/syscalltbl.sh b/scripts/syscalltbl.sh
index 6abe143889ef..6a903b87a7c2 100755
--- a/scripts/syscalltbl.sh
+++ b/scripts/syscalltbl.sh
@@ -54,7 +54,7 @@ nxt=0
grep -E "^[0-9]+[[:space:]]+$abis" "$infile" | {
- while read nr abi name native compat ; do
+ while read nr abi name native compat noreturn; do
if [ $nxt -gt $nr ]; then
echo "error: $infile: syscall table is not sorted or duplicates the same syscall number" >&2
@@ -66,7 +66,21 @@ grep -E "^[0-9]+[[:space:]]+$abis" "$infile" | {
nxt=$((nxt + 1))
done
- if [ -n "$compat" ]; then
+ if [ "$compat" = "-" ]; then
+ unset compat
+ fi
+
+ if [ -n "$noreturn" ]; then
+ if [ "$noreturn" != "noreturn" ]; then
+ echo "error: $infile: invalid string \"$noreturn\" in 'noreturn' column"
+ exit 1
+ fi
+ if [ -n "$compat" ]; then
+ echo "__SYSCALL_COMPAT_NORETURN($nr, $native, $compat)"
+ else
+ echo "__SYSCALL_NORETURN($nr, $native)"
+ fi
+ elif [ -n "$compat" ]; then
echo "__SYSCALL_WITH_COMPAT($nr, $native, $compat)"
elif [ -n "$native" ]; then
echo "__SYSCALL($nr, $native)"
diff --git a/tools/objtool/noreturns.h b/tools/objtool/noreturns.h
index 7ebf29c91184..1e8141ef1b15 100644
--- a/tools/objtool/noreturns.h
+++ b/tools/objtool/noreturns.h
@@ -7,12 +7,16 @@
* Yes, this is unfortunate. A better solution is in the works.
*/
NORETURN(__fortify_panic)
+NORETURN(__ia32_sys_exit)
+NORETURN(__ia32_sys_exit_group)
NORETURN(__kunit_abort)
NORETURN(__module_put_and_kthread_exit)
NORETURN(__reiserfs_panic)
NORETURN(__stack_chk_fail)
NORETURN(__tdx_hypercall_failed)
NORETURN(__ubsan_handle_builtin_unreachable)
+NORETURN(__x64_sys_exit)
+NORETURN(__x64_sys_exit_group)
NORETURN(arch_cpu_idle_dead)
NORETURN(bch2_trans_in_restart_error)
NORETURN(bch2_trans_restart_error)
--
2.45.1On Tue, Jun 25, 2024 at 11:02:00PM -0700, Josh Poimboeuf wrote:
> The direct-call syscall dispatch function doesn't know that the exit()
> and exit_group() syscall handlers don't return, so the call sites aren't
> optimized accordingly.
>
> Fix that by marking the exit syscall declarations __noreturn.
>
> Fixes the following warnings:
>
> vmlinux.o: warning: objtool: x64_sys_call+0x2804: __x64_sys_exit() is missing a __noreturn annotation
> vmlinux.o: warning: objtool: ia32_sys_call+0x29b6: __ia32_sys_exit_group() is missing a __noreturn annotation
>
> Fixes: 7390db8aea0d ("x86/bhi: Add support for clearing branch history at syscall entry")
> Reported-by: "Paul E. McKenney" <paulmck@kernel.org>
> Closes: https://lkml.kernel.org/lkml/6dba9b32-db2c-4e6d-9500-7a08852f17a3@paulmck-laptop
This here talks about
1e3ad78334a6 ("x86/syscall: Don't force use of indirect calls for system calls")
being the culprit.
But Fixes points to something unrelated...?
In any case, I won't send this to Linus now as urgent material unless someone
presents a reasonable argument for it...
Thx.
--
Regards/Gruss,
Boris.
https://people.kernel.org/tglx/notes-about-netiquette
On Thu, Jun 27, 2024 at 09:26:34AM +0200, Borislav Petkov wrote:
> On Tue, Jun 25, 2024 at 11:02:00PM -0700, Josh Poimboeuf wrote:
> > The direct-call syscall dispatch function doesn't know that the exit()
> > and exit_group() syscall handlers don't return, so the call sites aren't
> > optimized accordingly.
> >
> > Fix that by marking the exit syscall declarations __noreturn.
> >
> > Fixes the following warnings:
> >
> > vmlinux.o: warning: objtool: x64_sys_call+0x2804: __x64_sys_exit() is missing a __noreturn annotation
> > vmlinux.o: warning: objtool: ia32_sys_call+0x29b6: __ia32_sys_exit_group() is missing a __noreturn annotation
> >
> > Fixes: 7390db8aea0d ("x86/bhi: Add support for clearing branch history at syscall entry")
> > Reported-by: "Paul E. McKenney" <paulmck@kernel.org>
> > Closes: https://lkml.kernel.org/lkml/6dba9b32-db2c-4e6d-9500-7a08852f17a3@paulmck-laptop
>
> This here talks about
>
> 1e3ad78334a6 ("x86/syscall: Don't force use of indirect calls for system calls")
>
> being the culprit.
>
> But Fixes points to something unrelated...?
Ah yeah, it should be
Fixes: 1e3ad78334a6 ("x86/syscall: Don't force use of indirect calls for system calls")
--
Josh
On Thu, Jun 27, 2024 at 09:26:34AM +0200, Borislav Petkov wrote:
> On Tue, Jun 25, 2024 at 11:02:00PM -0700, Josh Poimboeuf wrote:
> > The direct-call syscall dispatch function doesn't know that the exit()
> > and exit_group() syscall handlers don't return, so the call sites aren't
> > optimized accordingly.
> >
> > Fix that by marking the exit syscall declarations __noreturn.
> >
> > Fixes the following warnings:
> >
> > vmlinux.o: warning: objtool: x64_sys_call+0x2804: __x64_sys_exit() is missing a __noreturn annotation
> > vmlinux.o: warning: objtool: ia32_sys_call+0x29b6: __ia32_sys_exit_group() is missing a __noreturn annotation
> >
> > Fixes: 7390db8aea0d ("x86/bhi: Add support for clearing branch history at syscall entry")
> > Reported-by: "Paul E. McKenney" <paulmck@kernel.org>
> > Closes: https://lkml.kernel.org/lkml/6dba9b32-db2c-4e6d-9500-7a08852f17a3@paulmck-laptop
>
> This here talks about
>
> 1e3ad78334a6 ("x86/syscall: Don't force use of indirect calls for system calls")
>
> being the culprit.
>
> But Fixes points to something unrelated...?
>
> In any case, I won't send this to Linus now as urgent material unless someone
> presents a reasonable argument for it...
Its being in -next now and going into the upcoming merge window works
just fine for me, thank you!
Thanx, Paul
On Tue, Jun 25, 2024 at 11:02:00PM -0700, Josh Poimboeuf wrote:
> The direct-call syscall dispatch function doesn't know that the exit()
> and exit_group() syscall handlers don't return, so the call sites aren't
> optimized accordingly.
>
> Fix that by marking the exit syscall declarations __noreturn.
>
> Fixes the following warnings:
>
> vmlinux.o: warning: objtool: x64_sys_call+0x2804: __x64_sys_exit() is missing a __noreturn annotation
> vmlinux.o: warning: objtool: ia32_sys_call+0x29b6: __ia32_sys_exit_group() is missing a __noreturn annotation
>
> Fixes: 7390db8aea0d ("x86/bhi: Add support for clearing branch history at syscall entry")
> Reported-by: "Paul E. McKenney" <paulmck@kernel.org>
> Closes: https://lkml.kernel.org/lkml/6dba9b32-db2c-4e6d-9500-7a08852f17a3@paulmck-laptop
> Tested-by: Paul E. McKenney <paulmck@kernel.org>
> Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
> ---
> arch/x86/entry/syscall_32.c | 10 ++++++----
> arch/x86/entry/syscall_64.c | 9 ++++++---
> arch/x86/entry/syscall_x32.c | 7 +++++--
> arch/x86/entry/syscalls/syscall_32.tbl | 6 +++---
> arch/x86/entry/syscalls/syscall_64.tbl | 6 +++---
> arch/x86/um/sys_call_table_32.c | 10 ++++++----
> arch/x86/um/sys_call_table_64.c | 11 +++++++----
> scripts/syscalltbl.sh | 18 ++++++++++++++++--
> tools/objtool/noreturns.h | 4 ++++
> 9 files changed, 56 insertions(+), 25 deletions(-)
Hi,
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