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Groups > linux.kernel > #1459881
| From | tip-bot for Borislav Petkov <tipbot@zytor.com> |
|---|---|
| Newsgroups | linux.kernel |
| Subject | [tip:x86/urgent] x86/entry: Clarify the RF saving/restoring situation with SYSCALL/SYSRET |
| Date | 2016-08-10 22:50 +0200 |
| Message-ID | <s4IBP-1DK-3@gated-at.bofh.it> (permalink) |
| References | <s27ZM-5m7-3@gated-at.bofh.it> |
| Organization | linux.* mail to news gateway |
Commit-ID: 3e035305875cfa8a58c1ca573d0cfa6a7f201f27 Gitweb: http://git.kernel.org/tip/3e035305875cfa8a58c1ca573d0cfa6a7f201f27 Author: Borislav Petkov <bp@alien8.de> AuthorDate: Wed, 3 Aug 2016 19:14:29 +0200 Committer: Ingo Molnar <mingo@kernel.org> CommitDate: Wed, 10 Aug 2016 15:53:43 +0200 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 <bp@suse.de> Acked-by: Andy Lutomirski <luto@amacapital.net> Cc: Andy Lutomirski <luto@kernel.org> Cc: Borislav Petkov <bp@alien8.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: Thomas Gleixner <tglx@linutronix.de> Link: http://lkml.kernel.org/r/20160803171429.GA2590@nazgul.tnic Signed-off-by: Ingo Molnar <mingo@kernel.org> --- arch/x86/entry/entry_64.S | 14 +++++++++----- 1 file changed, 9 insertions(+), 5 deletions(-) diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S index 9f85827..d172c61 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
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[PATCH] x86/entry: Clarify the RF saving/restoring situation with SYSCALL/SYSRET Borislav Petkov <bp@alien8.de> - 2016-08-03 12:30 +0200
Re: [PATCH] x86/entry: Clarify the RF saving/restoring situation with SYSCALL/SYSRET Andy Lutomirski <luto@amacapital.net> - 2016-08-03 18:50 +0200
Re: [PATCH] x86/entry: Clarify the RF saving/restoring situation with SYSCALL/SYSRET Borislav Petkov <bp@alien8.de> - 2016-08-03 19:20 +0200
Re: [PATCH] x86/entry: Clarify the RF saving/restoring situation with SYSCALL/SYSRET Andy Lutomirski <luto@amacapital.net> - 2016-08-03 19:30 +0200
Re: [PATCH] x86/entry: Clarify the RF saving/restoring situation with SYSCALL/SYSRET Borislav Petkov <bp@alien8.de> - 2016-08-03 20:10 +0200
[tip:x86/urgent] x86/entry: Clarify the RF saving/restoring situation with SYSCALL/SYSRET tip-bot for Borislav Petkov <tipbot@zytor.com> - 2016-08-10 22:50 +0200
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