diff options
| author | Borislav Petkov <[email protected]> | 2016-08-03 19:14:29 +0200 |
|---|---|---|
| committer | Ingo Molnar <[email protected]> | 2016-08-10 15:53:43 +0200 |
| commit | 3e035305875cfa8a58c1ca573d0cfa6a7f201f27 (patch) | |
| tree | 36abe0cf08dfd0b70504ce5c23c167e767a6dd83 | |
| parent | 5cf0791da5c162ebc14b01eb01631cfa7ed4fa6e (diff) | |
x86/entry: Clarify the RF saving/restoring situation with SYSCALL/SYSRET
Clarify why exactly RF cannot be restored properly by SYSRET to avoid
confusion.
No functionality change.
Signed-off-by: Borislav Petkov <[email protected]>
Acked-by: Andy Lutomirski <[email protected]>
Cc: Andy Lutomirski <[email protected]>
Cc: Borislav Petkov <[email protected]>
Cc: Brian Gerst <[email protected]>
Cc: Denys Vlasenko <[email protected]>
Cc: H. Peter Anvin <[email protected]>
Cc: Josh Poimboeuf <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Ingo Molnar <[email protected]>
| -rw-r--r-- | arch/x86/entry/entry_64.S | 14 |
1 files changed, 9 insertions, 5 deletions
diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S index 9f85827db24e..d172c619c449 100644 --- a/arch/x86/entry/entry_64.S +++ b/arch/x86/entry/entry_64.S @@ -288,11 +288,15 @@ return_from_SYSCALL_64: jne opportunistic_sysret_failed /* - * SYSRET can't restore RF. SYSRET can restore TF, but unlike IRET, - * restoring TF results in a trap from userspace immediately after - * SYSRET. This would cause an infinite loop whenever #DB happens - * with register state that satisfies the opportunistic SYSRET - * conditions. For example, single-stepping this user code: + * SYSCALL clears RF when it saves RFLAGS in R11 and SYSRET cannot + * restore RF properly. If the slowpath sets it for whatever reason, we + * need to restore it correctly. + * + * SYSRET can restore TF, but unlike IRET, restoring TF results in a + * trap from userspace immediately after SYSRET. This would cause an + * infinite loop whenever #DB happens with register state that satisfies + * the opportunistic SYSRET conditions. For example, single-stepping + * this user code: * * movq $stuck_here, %rcx * pushfq |