[PATCH 5.4 110/154] x86/entry: Fix ORC unwinder for PUSH_REGS with save_ret=1

Greg Kroah-Hartman
2025-04-08T12:07:15Z

From: Jann Horn <jannh@google.com>

[ Upstream commit 57e2428f8df8263275344566e02c277648a4b7f1 ]

PUSH_REGS with save_ret=1 is used by interrupt entry helper functions that
initially start with a UNWIND_HINT_FUNC ORC state.

However, save_ret=1 means that we clobber the helper function's return
address (and then later restore the return address further down on the
stack); after that point, the only thing on the stack we can unwind through
is the IRET frame, so use UNWIND_HINT_IRET_REGS until we have a full
pt_regs frame.

( An alternate approach would be to move the pt_regs->di overwrite down
such that it is the final step of pt_regs setup; but I don't want to
rearrange entry code just to make unwinding a tiny bit more elegant. )

Fixes: 9e809d15d6b6 ("x86/entry: Reduce the code footprint of the 'idtentry' macro")
Signed-off-by: Jann Horn <jannh@google.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Juergen Gross <jgross@suse.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Kees Cook <keescook@chromium.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Link: https://lore.kernel.org/r/20250325-2025-03-unwind-fixes-v1-1-acd774364768@google.com
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
arch/x86/entry/calling.h | 2 ++
1 file changed, 2 insertions(+)

diff --git a/arch/x86/entry/calling.h b/arch/x86/entry/calling.h
index 29e5675c6d4f2..6819ace46d8d2 100644
--- a/arch/x86/entry/calling.h
+++ b/arch/x86/entry/calling.h
@@ -104,6 +104,8 @@ For 32-bit we have the following conventions - kernel is built with
pushq %rsi /* pt_regs->si */
movq 8(%rsp), %rsi /* temporarily store the return address in %rsi */
movq %rdi, 8(%rsp) /* pt_regs->di (overwriting original return address) */
+ /* We just clobbered the return address - use the IRET frame for unwinding: */
+ UNWIND_HINT_IRET_REGS offset=3*8
.else
pushq %rdi /* pt_regs->di */
pushq %rsi /* pt_regs->si */
--
2.39.5