stub_sigreturn ignores old values of pt_regs->REG for all general-purpose
registers, it sets them to values saved on userspace
signal stack.
Which is hardly surprising - it would be a bug if it would use pt_regs->REG.
sigreturn must restore all registers.
Therefore, SAVE_EXTRA_REGS in it ought to be redundant.
It is a leftover from the time SAVE_EXTRA_REGS wasn't only saving registers,
but it also was extending stack to "full" pt_regs.
Delete this SAVE_EXTRA_REGS.
Run-tested.
Signed-off-by: Denys Vlasenko <dvlas...@redhat.com>
CC: Linus Torvalds <torva...@linux-foundation.org>
CC: Steven Rostedt <rost...@goodmis.org>
CC: Ingo Molnar <mi...@kernel.org>
CC: Borislav Petkov <b...@alien8.de>
CC: "H. Peter Anvin" <h...@zytor.com>
CC: Andy Lutomirski <l...@amacapital.net>
CC: Oleg Nesterov <o...@redhat.com>
CC: Frederic Weisbecker <fweis...@gmail.com>
CC: Alexei Starovoitov <a...@plumgrid.com>
CC: Will Drewry <w...@chromium.org>
CC: Kees Cook <keesc...@chromium.org>
CC: x...@kernel.org
CC: linux-kernel@vger.kernel.org
---
arch/x86/kernel/entry_64.S | 9 +++++++--
1 file changed, 7 insertions(+), 2 deletions(-)
diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S
index ec51598..1cf245d 100644
--- a/arch/x86/kernel/entry_64.S
+++ b/arch/x86/kernel/entry_64.S
@@ -447,7 +447,12 @@ ENTRY(stub_rt_sigreturn)
CFI_STARTPROC
addq $8, %rsp
DEFAULT_FRAME 0
- SAVE_EXTRA_REGS
+ /*
+ * Despite RESTORE_EXTRA_REGS in return_from_stub,
+ * no need to SAVE_EXTRA_REGS here:
+ * sys_rt_sigreturn overwrites all general purpose pt_regs->REGs
+ * on stack, for RESTORE_{EXTRA,C}_REGS to pick them up.
+ */
call sys_rt_sigreturn
jmp return_from_stub
CFI_ENDPROC
@@ -458,7 +463,7 @@ ENTRY(stub_x32_rt_sigreturn)
CFI_STARTPROC
addq $8, %rsp
DEFAULT_FRAME 0
- SAVE_EXTRA_REGS
+ /* No need to SAVE_EXTRA_REGS */
call sys32_x32_rt_sigreturn
jmp return_from_stub
CFI_ENDPROC
--
1.8.1.4
--
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