Commit-ID: eb2a54c3271cb6443ae93ec44a91687b60c559a3 Gitweb: http://git.kernel.org/tip/eb2a54c3271cb6443ae93ec44a91687b60c559a3 Author: Andy Lutomirski <[email protected]> AuthorDate: Sun, 31 Jan 2016 09:33:27 -0800 Committer: Ingo Molnar <[email protected]> CommitDate: Mon, 1 Feb 2016 08:53:25 +0100
x86/entry/64: Fix fast-path syscall return register state I was fishing RIP (i.e. RCX) out of pt_regs->cx and RFLAGS (i.e. R11) out of pt_regs->r11. While it usually worked (pt_regs started out with CX == IP and R11 == FLAGS), it was very fragile. In particular, it broke sys_iopl() because sys_iopl() forgot to mark itself as using ptregs. Undo that part of the syscall rework. There was no compelling reason to do it this way. While I'm at it, load RCX and R11 before the other regs to be a little friendlier to the CPU, as they will be the first of the reloaded registers to be used. Reported-and-tested-by: Borislav Petkov <[email protected]> Signed-off-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: Linus Torvalds <[email protected]> Cc: Peter Zijlstra <[email protected]> Cc: Thomas Gleixner <[email protected]> Fixes: 1e423bff959e x86/entry/64: ("Migrate the 64-bit syscall slow path to C") Link: http://lkml.kernel.org/r/a85f8360c397e48186a9bc3e565ad74307a7b011.1454261517.git.l...@kernel.org Signed-off-by: Ingo Molnar <[email protected]> --- arch/x86/entry/entry_64.S | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S index 9f7bb80..70eadb0 100644 --- a/arch/x86/entry/entry_64.S +++ b/arch/x86/entry/entry_64.S @@ -212,7 +212,9 @@ entry_SYSCALL_64_fastpath: LOCKDEP_SYS_EXIT TRACE_IRQS_ON /* user mode is traced as IRQs on */ - RESTORE_C_REGS + movq RIP(%rsp), %rcx + movq EFLAGS(%rsp), %r11 + RESTORE_C_REGS_EXCEPT_RCX_R11 movq RSP(%rsp), %rsp USERGS_SYSRET64
