[PATCH] x86/selftests: add clobbers for int80 on x86_64
From: Dmitry Safonov
Date: Fri Feb 10 2017 - 06:58:41 EST
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 <shuah@xxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
Cc: Andy Lutomirski <luto@xxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxx>
Cc: x86@xxxxxxxxxx
Cc: linux-kselftest@xxxxxxxxxxxxxxx
Signed-off-by: Dmitry Safonov <dsafonov@xxxxxxxxxxxxx>
---
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