Hi Sasha,
I would object including this to stable tree: 1. It's selftest fixup 2. I have never saw selftests failing because of it (but it's possible) I saw this in CRIU (Checkpoint Restore In Userspace) project triggering, so I've fixed the selftests, mostly for documentation reasons - as people in userspace can reuse this code and think it's good and will just work after copy-paste (which is not the case).
So, this patch doesn't look urgent to include it in -stable kernel.
Thanks, Dmitry
2017-11-29 17:21 GMT+00:00 alexander.levin@verizon.com:
From: Dmitry Safonov dsafonov@virtuozzo.com
[ Upstream commit 2a4d0c627f5374f365a873dea4e10ae0bb437680 ]
Kernel erases R8..R11 registers prior returning to userspace from int80:
https://lkml.org/lkml/2009/10/1/164
GCC can reuse these registers and doesn't expect them to change during syscall invocation. I met this kind of bug in CRIU once GCC 6.1 and CLANG stored local variables in those registers and the kernel zerofied them during syscall:
https://github.com/xemul/criu/commit/990d33f1a1cdd17bca6c2eb059ab3be2564f7fa...
By that reason I suggest to add those registers to clobbers in selftests. Also, as noted by Andy - removed unneeded clobber for flags in INT $0x80 inline asm.
Signed-off-by: Dmitry Safonov dsafonov@virtuozzo.com Acked-by: Andy Lutomirski luto@kernel.org Cc: 0x7f454c46@gmail.com Cc: Borislav Petkov bp@alien8.de Cc: Borislav Petkov bp@suse.de Cc: Brian Gerst brgerst@gmail.com Cc: Denys Vlasenko dvlasenk@redhat.com Cc: H. Peter Anvin hpa@zytor.com Cc: Josh Poimboeuf jpoimboe@redhat.com Cc: Linus Torvalds torvalds@linux-foundation.org Cc: Peter Zijlstra peterz@infradead.org Cc: Shuah Khan shuah@kernel.org Cc: Thomas Gleixner tglx@linutronix.de Cc: linux-kselftest@vger.kernel.org Link: http://lkml.kernel.org/r/20170213101336.20486-1-dsafonov@virtuozzo.com Signed-off-by: Ingo Molnar mingo@kernel.org Signed-off-by: Sasha Levin alexander.levin@verizon.com
tools/testing/selftests/x86/fsgsbase.c | 2 +- tools/testing/selftests/x86/ldt_gdt.c | 16 +++++++++++----- tools/testing/selftests/x86/ptrace_syscall.c | 3 ++- tools/testing/selftests/x86/single_step_syscall.c | 5 ++++- 4 files changed, 18 insertions(+), 8 deletions(-)
diff --git a/tools/testing/selftests/x86/fsgsbase.c b/tools/testing/selftests/x86/fsgsbase.c index 9b4610c6d3fb..f249e042b3b5 100644 --- a/tools/testing/selftests/x86/fsgsbase.c +++ b/tools/testing/selftests/x86/fsgsbase.c @@ -245,7 +245,7 @@ void do_unexpected_base(void) long ret; asm volatile ("int $0x80" : "=a" (ret) : "a" (243), "b" (low_desc)
: "flags");
: "r8", "r9", "r10", "r11"); memcpy(&desc, low_desc, sizeof(desc)); munmap(low_desc, sizeof(desc));diff --git a/tools/testing/selftests/x86/ldt_gdt.c b/tools/testing/selftests/x86/ldt_gdt.c index e717fed80219..b9a22f18566a 100644 --- a/tools/testing/selftests/x86/ldt_gdt.c +++ b/tools/testing/selftests/x86/ldt_gdt.c @@ -45,6 +45,12 @@ #define AR_DB (1 << 22) #define AR_G (1 << 23)
+#ifdef __x86_64__ +# define INT80_CLOBBERS "r8", "r9", "r10", "r11" +#else +# define INT80_CLOBBERS +#endif
static int nerrs;
/* Points to an array of 1024 ints, each holding its own index. */ @@ -634,7 +640,7 @@ static int invoke_set_thread_area(void) asm volatile ("int $0x80" : "=a" (ret), "+m" (low_user_desc) : "a" (243), "b" (low_user_desc)
: "flags");
: INT80_CLOBBERS); return ret;}
@@ -703,7 +709,7 @@ static void test_gdt_invalidation(void) "+a" (eax) : "m" (low_user_desc_clear), [arg1] "r" ((unsigned int)(unsigned long)low_user_desc_clear)
: "flags");
: INT80_CLOBBERS); if (sel != 0) { result = "FAIL";@@ -734,7 +740,7 @@ static void test_gdt_invalidation(void) "+a" (eax) : "m" (low_user_desc_clear), [arg1] "r" ((unsigned int)(unsigned long)low_user_desc_clear)
: "flags");
: INT80_CLOBBERS); if (sel != 0) { result = "FAIL";@@ -767,7 +773,7 @@ static void test_gdt_invalidation(void) "+a" (eax) : "m" (low_user_desc_clear), [arg1] "r" ((unsigned int)(unsigned long)low_user_desc_clear)
: "flags");
: INT80_CLOBBERS);#ifdef __x86_64__ syscall(SYS_arch_prctl, ARCH_GET_FS, &new_base); @@ -820,7 +826,7 @@ static void test_gdt_invalidation(void) "+a" (eax) : "m" (low_user_desc_clear), [arg1] "r" ((unsigned int)(unsigned long)low_user_desc_clear)
: "flags");
: INT80_CLOBBERS);#ifdef __x86_64__ syscall(SYS_arch_prctl, ARCH_GET_GS, &new_base); diff --git a/tools/testing/selftests/x86/ptrace_syscall.c b/tools/testing/selftests/x86/ptrace_syscall.c index b037ce9cf116..eaea92439708 100644 --- a/tools/testing/selftests/x86/ptrace_syscall.c +++ b/tools/testing/selftests/x86/ptrace_syscall.c @@ -58,7 +58,8 @@ static void do_full_int80(struct syscall_args32 *args) asm volatile ("int $0x80" : "+a" (args->nr), "+b" (args->arg0), "+c" (args->arg1), "+d" (args->arg2),
"+S" (args->arg3), "+D" (args->arg4), "+r" (bp));
"+S" (args->arg3), "+D" (args->arg4), "+r" (bp): : "r8", "r9", "r10", "r11"); args->arg5 = bp;#else sys32_helper(args, int80_and_ret); diff --git a/tools/testing/selftests/x86/single_step_syscall.c b/tools/testing/selftests/x86/single_step_syscall.c index 50c26358e8b7..a48da95c18fd 100644 --- a/tools/testing/selftests/x86/single_step_syscall.c +++ b/tools/testing/selftests/x86/single_step_syscall.c @@ -56,9 +56,11 @@ static volatile sig_atomic_t sig_traps; #ifdef __x86_64__ # define REG_IP REG_RIP # define WIDTH "q" +# define INT80_CLOBBERS "r8", "r9", "r10", "r11" #else # define REG_IP REG_EIP # define WIDTH "l" +# define INT80_CLOBBERS #endif
static unsigned long get_eflags(void) @@ -140,7 +142,8 @@ int main()
printf("[RUN]\tSet TF and check int80\n"); set_eflags(get_eflags() | X86_EFLAGS_TF);
asm volatile ("int $0x80" : "=a" (tmp) : "a" (SYS_getpid));
asm volatile ("int $0x80" : "=a" (tmp) : "a" (SYS_getpid): INT80_CLOBBERS); check_result(); /*-- 2.11.0