diff options
| author | Andy Lutomirski <[email protected]> | 2015-01-16 16:19:27 -0800 |
|---|---|---|
| committer | Ingo Molnar <[email protected]> | 2015-01-17 11:02:53 +0100 |
| commit | 0fcedc8631ec28ca25d3c0b116e8fa0c19dd5f6d (patch) | |
| tree | c2e9f6e636e0ea08bef431d15096ad3efb9ae5a2 | |
| parent | f800c25b7a762d445ba1439a2428c8362157eba6 (diff) | |
x86_64 entry: Fix RCX for ptraced syscalls
The int_ret_from_sys_call and syscall tracing code disagrees
with the sysret path as to the value of RCX.
The Intel SDM, the AMD APM, and my laptop all agree that sysret
returns with RCX == RIP. The syscall tracing code does not
respect this property.
For example, this program:
int main()
{
extern const char syscall_rip[];
unsigned long rcx = 1;
unsigned long orig_rcx = rcx;
asm ("mov $-1, %%eax\n\t"
"syscall\n\t"
"syscall_rip:"
: "+c" (rcx) : : "r11");
printf("syscall: RCX = %lX RIP = %lX orig RCX = %lx\n",
rcx, (unsigned long)syscall_rip, orig_rcx);
return 0;
}
prints:
syscall: RCX = 400556 RIP = 400556 orig RCX = 1
Running it under strace gives this instead:
syscall: RCX = FFFFFFFFFFFFFFFF RIP = 400556 orig RCX = 1
This changes FIXUP_TOP_OF_STACK to match sysret, causing the
test to show RCX == RIP even under strace.
It looks like this is a partial revert of:
88e4bc32686e ("[PATCH] x86-64 architecture specific sync for 2.5.8")
from the historic git tree.
Signed-off-by: Andy Lutomirski <[email protected]>
Cc: Frederic Weisbecker <[email protected]>
Cc: Oleg Nesterov <[email protected]>
Cc: Borislav Petkov <[email protected]>
Cc: Rik van Riel <[email protected]>
Cc: Linus Torvalds <[email protected]>
Link: http://lkml.kernel.org/r/c9a418c3dc3993cb88bb7773800225fd318a4c67.1421453410.git.luto@amacapital.net
Signed-off-by: Ingo Molnar <[email protected]>
| -rw-r--r-- | arch/x86/kernel/entry_64.S | 3 |
1 files changed, 2 insertions, 1 deletions
diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S index 9ebaf63ba182..c653dc437e6b 100644 --- a/arch/x86/kernel/entry_64.S +++ b/arch/x86/kernel/entry_64.S @@ -143,7 +143,8 @@ ENDPROC(native_usergs_sysret64) movq \tmp,RSP+\offset(%rsp) movq $__USER_DS,SS+\offset(%rsp) movq $__USER_CS,CS+\offset(%rsp) - movq $-1,RCX+\offset(%rsp) + movq RIP+\offset(%rsp),\tmp /* get rip */ + movq \tmp,RCX+\offset(%rsp) /* copy it to rcx as sysret would do */ movq R11+\offset(%rsp),\tmp /* get eflags */ movq \tmp,EFLAGS+\offset(%rsp) .endm |