Kernel erases R8..R11 registers prior returning to userspace from int80: https://lkml.org/lkml/2009/10/1/164
GCC can reuse this 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/990d33f1a1cdd17bca6c2eb059ab3be2564f7fa2 By that reason I suggest to add those registers to clobbers in selftests. Cc: Shuah Khan <[email protected]> Cc: Thomas Gleixner <[email protected]> Cc: Ingo Molnar <[email protected]> Cc: "H. Peter Anvin" <[email protected]> Cc: Andy Lutomirski <[email protected]> Cc: Borislav Petkov <[email protected]> Cc: [email protected] Cc: [email protected] Signed-off-by: Dmitry Safonov <[email protected]> --- tools/testing/selftests/x86/fsgsbase.c | 2 +- tools/testing/selftests/x86/iopl.c | 10 ++++++++-- 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 ++++- 5 files changed, 26 insertions(+), 10 deletions(-) diff --git a/tools/testing/selftests/x86/fsgsbase.c b/tools/testing/selftests/x86/fsgsbase.c index 5b2b4b3c634c..059b06b2d81d 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"); + : "flags", "r8", "r9", "r10", "r11"); memcpy(&desc, low_desc, sizeof(desc)); munmap(low_desc, sizeof(desc)); diff --git a/tools/testing/selftests/x86/iopl.c b/tools/testing/selftests/x86/iopl.c index c496ca97bc18..98236a233db8 100644 --- a/tools/testing/selftests/x86/iopl.c +++ b/tools/testing/selftests/x86/iopl.c @@ -19,6 +19,12 @@ #include <sched.h> #include <sys/io.h> +#ifdef __x86_64__ +# define INT80_CLOBBERS "r8", "r9", "r10", "r11" +#else +# define INT80_CLOBBERS +#endif + static int nerrs = 0; static void sethandler(int sig, void (*handler)(int, siginfo_t *, void *), @@ -70,7 +76,7 @@ int main(void) err(1, "iopl"); printf("[RUN]\tchild: write to 0x80\n"); - asm volatile ("outb %%al, $0x80" : : "a" (0)); + asm volatile ("outb %%al, $0x80" : : "a" (0) : INT80_CLOBBERS); return 0; } else { @@ -93,7 +99,7 @@ int main(void) if (sigsetjmp(jmpbuf, 1) != 0) { printf("[OK]\twrite was denied\n"); } else { - asm volatile ("outb %%al, $0x80" : : "a" (0)); + asm volatile ("outb %%al, $0x80" : : "a" (0) : INT80_CLOBBERS); printf("[FAIL]\twrite was allowed\n"); nerrs++; } diff --git a/tools/testing/selftests/x86/ldt_gdt.c b/tools/testing/selftests/x86/ldt_gdt.c index 4af47079cf04..dfdabd1f3083 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 "flags", "r8", "r9", "r10", "r11" +#else +# define INT80_CLOBBERS "flags" +#endif + static int nerrs; /* Points to an array of 1024 ints, each holding its own index. */ @@ -588,7 +594,7 @@ 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; } @@ -657,7 +663,7 @@ 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"; @@ -688,7 +694,7 @@ 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"; @@ -721,7 +727,7 @@ 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); @@ -774,7 +780,7 @@ 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(); /* -- 2.11.1
