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Subject[PATCH V2 2/4] x86/entry: directly switch to kernel stack when .Lerror_bad_iret
Date
Directly copy pt_regs to kernel stack when .Lerror_bad_iret.
Directly switch to kernel stack when .Lerror_bad_iret.

We can see that entry_64.S do the following things back to back
when .Lerror_bad_iret:
call fixup_bad_iret(), switch to sp0 stack with pt_regs copied
call sync_regs(), switch to kernel stack with pt_regs copied

So we can do the all things together in fixup_bad_iret().

After this patch, fixup_bad_iret() is restored to the behavior before
7f2590a110b8("x86/entry/64: Use a per-CPU trampoline stack for IDT entries")

Signed-off-by: Lai Jiangshan <laijs@linux.alibaba.com>
---
arch/x86/entry/entry_64.S | 13 ++-----------
arch/x86/kernel/traps.c | 9 ++++-----
2 files changed, 6 insertions(+), 16 deletions(-)

diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
index b524ff3499d0..6f8963072ed0 100644
--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -915,16 +915,6 @@ SYM_CODE_START_LOCAL(error_entry)
ENCODE_FRAME_POINTER 8
ret

-.Lerror_entry_from_usermode_after_swapgs:
- /* Put us onto the real thread stack. */
- popq %r12 /* save return addr in %12 */
- movq %rsp, %rdi /* arg0 = pt_regs pointer */
- call sync_regs
- movq %rax, %rsp /* switch stack */
- ENCODE_FRAME_POINTER
- pushq %r12
- ret
-
.Lerror_entry_done_lfence:
FENCE_SWAPGS_KERNEL_ENTRY
.Lerror_entry_done:
@@ -978,7 +968,8 @@ SYM_CODE_START_LOCAL(error_entry)
mov %rsp, %rdi
call fixup_bad_iret
mov %rax, %rsp
- jmp .Lerror_entry_from_usermode_after_swapgs
+ ENCODE_FRAME_POINTER 8
+ ret
SYM_CODE_END(error_entry)

SYM_CODE_START_LOCAL(error_return)
diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
index 50fb9cd5be97..053a15717bfd 100644
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -669,13 +669,12 @@ struct bad_iret_stack *fixup_bad_iret(struct bad_iret_stack *s)
/*
* This is called from entry_64.S early in handling a fault
* caused by a bad iret to user mode. To handle the fault
- * correctly, we want to move our stack frame to where it would
- * be had we entered directly on the entry stack (rather than
- * just below the IRET frame) and we want to pretend that the
- * exception came from the IRET target.
+ * correctly, we want to move our stack frame to kernel stack
+ * (rather than just below the IRET frame) and we want to
+ * pretend that the exception came from the IRET target.
*/
struct bad_iret_stack tmp, *new_stack =
- (struct bad_iret_stack *)__this_cpu_read(cpu_tss_rw.x86_tss.sp0) - 1;
+ (struct bad_iret_stack *)__this_cpu_read(cpu_current_top_of_stack) - 1;

/* Copy the IRET target to the temporary storage. */
memcpy(&tmp.regs.ip, (void *)s->regs.sp, 5*8);
--
2.20.1
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