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Commit 2a4d0c62 authored by Dmitry Safonov's avatar Dmitry Safonov Committed by Ingo Molnar
Browse files

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: default avatarDmitry Safonov <dsafonov@virtuozzo.com>
Acked-by: default avatarAndy 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: default avatarIngo Molnar <mingo@kernel.org>
parent 11277aab

tools/testing/selftests/x86/fsgsbase.c

+1 −1
Original line number Diff line number Diff line
@@ -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));

tools/testing/selftests/x86/ldt_gdt.c

+11 −5
Original line number Diff line number Diff line
@@ -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);

tools/testing/selftests/x86/ptrace_syscall.c

+2 −1
Original line number Diff line number Diff line
@@ -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);

tools/testing/selftests/x86/single_step_syscall.c

+4 −1
Original line number Diff line number Diff line
@@ -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();



	/*