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 <[email protected]> CC: Linus Torvalds <[email protected]> CC: Steven Rostedt <[email protected]> CC: Ingo Molnar <[email protected]> CC: Borislav Petkov <[email protected]> CC: "H. Peter Anvin" <[email protected]> CC: Andy Lutomirski <[email protected]> CC: Oleg Nesterov <[email protected]> CC: Frederic Weisbecker <[email protected]> CC: Alexei Starovoitov <[email protected]> CC: Will Drewry <[email protected]> CC: Kees Cook <[email protected]> CC: [email protected] CC: [email protected] --- 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 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
