Commit eb2a54c3 authored by Andy Lutomirski's avatar Andy Lutomirski Committed by Ingo Molnar

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: default avatarBorislav Petkov <bp@suse.de>
Signed-off-by: default avatarAndy Lutomirski <luto@kernel.org>
Cc: Andy Lutomirski <luto@amacapital.net>
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: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Fixes: 1e423bff x86/entry/64: ("Migrate the 64-bit syscall slow path to C")
Link: http://lkml.kernel.org/r/a85f8360c397e48186a9bc3e565ad74307a7b011.1454261517.git.luto@kernel.orgSigned-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent b7765086
...@@ -212,7 +212,9 @@ entry_SYSCALL_64_fastpath: ...@@ -212,7 +212,9 @@ entry_SYSCALL_64_fastpath:
LOCKDEP_SYS_EXIT LOCKDEP_SYS_EXIT
TRACE_IRQS_ON /* user mode is traced as IRQs on */ 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 movq RSP(%rsp), %rsp
USERGS_SYSRET64 USERGS_SYSRET64
......
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