x86/selftests: Add clobbers for int80 on x86_64

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/990d33f1a1cdd17bca6c2eb059ab3be2564f7fa2

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>

diff --git a/tools/testing/selftests/x86/fsgsbase.c b/tools/testing/selftests/x86/fsgsbase.c
index 5b2b4b3c634ca17462730a7d3740fd698540a975..b4967d8752365545149274cf9e70b7717a826866 100644 (file)
--- 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 4af47079cf04305cec7e6a8d2aa0960a6fcfe352..f6121612e769f5600d1cc0920037ee4c6ee0bf92 100644 (file)
--- 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. */
@@ -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 b037ce9cf116b1da0ef57601f8f1840e45fcc775..eaea9243970840dab196cb1ddf84586e30803f0a 100644 (file)
--- 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 50c26358e8b7ec055000ead54c2c80c69b371a6f..a48da95c18fdf1f0ea46e7cb628ff9a9caba931b 100644 (file)
--- 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();
 
        /*