[PATCH 4.9 067/148] x86/selftests: Add clobbers for int80 on x86_64

Greg Kroah-Hartman
2017-12-12T12:57:53Z

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/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>
Signed-off-by: Sasha Levin <alexander.levin@verizon.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
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(-)

--- 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));

--- 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. */
@@ -649,7 +655,7 @@ 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;
}

@@ -718,7 +724,7 @@ 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";
@@ -749,7 +755,7 @@ 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";
@@ -782,7 +788,7 @@ 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);
@@ -835,7 +841,7 @@ 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);
--- 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
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);
--- 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();

/*