x86/entry/64: Fix an IRQ state error on ptregs-using syscalls
I messed up the IRQ state when jumping off the fast path due to
invocation of a ptregs-using syscall. This bug shouldn't have
had any impact yet, but it would have caused problems with
subsequent context tracking cleanups.
Reported-and-tested-by: Borislav Petkov <bp@suse.de>
Signed-off-by: Andy 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: 1e423bff959e x86/entry/64: ("Migrate the 64-bit syscall slow path to C")
Link: http://lkml.kernel.org/r/ab92cd365fb7b0a56869e920017790d96610fdca.1454261517.git.luto@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
index 567aa52..9f7bb80 100644
--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -191,8 +191,8 @@
/*
* This call instruction is handled specially in stub_ptregs_64.
- * It might end up jumping to the slow path. If it jumps, RAX is
- * clobbered.
+ * It might end up jumping to the slow path. If it jumps, RAX
+ * and all argument registers are clobbered.
*/
call *sys_call_table(, %rax, 8)
.Lentry_SYSCALL_64_after_fastpath_call:
@@ -315,17 +315,24 @@
ENTRY(stub_ptregs_64)
/*
* Syscalls marked as needing ptregs land here.
- * If we are on the fast path, we need to save the extra regs.
- * If we are on the slow path, the extra regs are already saved.
+ * If we are on the fast path, we need to save the extra regs,
+ * which we achieve by trying again on the slow path. If we are on
+ * the slow path, the extra regs are already saved.
*
* RAX stores a pointer to the C function implementing the syscall.
+ * IRQs are on.
*/
cmpq $.Lentry_SYSCALL_64_after_fastpath_call, (%rsp)
jne 1f
- /* Called from fast path -- pop return address and jump to slow path */
+ /*
+ * Called from fast path -- disable IRQs again, pop return address
+ * and jump to slow path
+ */
+ DISABLE_INTERRUPTS(CLBR_NONE)
+ TRACE_IRQS_OFF
popq %rax
- jmp entry_SYSCALL64_slow_path /* called from fast path */
+ jmp entry_SYSCALL64_slow_path
1:
/* Called from C */
