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.
Fixes: 1e423bff959e x86/entry/64: ("Migrate the 64-bit syscall slow path to C")
Signed-off-by: Andy Lutomirski <l...@kernel.org>
---
arch/x86/entry/entry_64.S | 19 +++++++++++++------
1 file changed, 13 insertions(+), 6 deletions(-)
diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
index 567aa522ac0a..9f7bb808035e 100644
--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -191,8 +191,8 @@ entry_SYSCALL_64_fastpath:
/*
* 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 @@ END(entry_SYSCALL_64)
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 */
--
2.5.0
