On Fri, Jun 24, 2016 at 11:35:13AM -0400, Brian Gerst wrote: > On Fri, Jun 24, 2016 at 11:30 AM, Josh Poimboeuf <jpoimboe@xxxxxxxxxx> wrote: > > On Thu, Jun 23, 2016 at 09:23:06PM -0700, Andy Lutomirski wrote: > >> If we call do_exit with a clean stack, we greatly reduce the risk of > >> recursive oopses due to stack overflow in do_exit, and we allow > >> do_exit to work even if we OOPS from an IST stack. The latter gives > >> us a much better chance of surviving long enough after we detect a > >> stack overflow to write out our logs. > >> > >> I intentionally separated this from the preceding patch that > >> disables do_exit-on-OOPS on IST stacks. This way, if we need to > >> revert this patch, we still end up in an acceptable state wrt stack > >> overflow handling. > >> > >> Signed-off-by: Andy Lutomirski <luto@xxxxxxxxxx> > >> --- > >> arch/x86/entry/entry_32.S | 11 +++++++++++ > >> arch/x86/entry/entry_64.S | 11 +++++++++++ > >> arch/x86/kernel/dumpstack.c | 13 +++++++++---- > >> 3 files changed, 31 insertions(+), 4 deletions(-) > >> > >> diff --git a/arch/x86/entry/entry_32.S b/arch/x86/entry/entry_32.S > >> index 983e5d3a0d27..0b56666e6039 100644 > >> --- a/arch/x86/entry/entry_32.S > >> +++ b/arch/x86/entry/entry_32.S > >> @@ -1153,3 +1153,14 @@ ENTRY(async_page_fault) > >> jmp error_code > >> END(async_page_fault) > >> #endif > >> + > >> +ENTRY(rewind_stack_do_exit) > >> + /* Prevent any naive code from trying to unwind to our caller. */ > >> + xorl %ebp, %ebp > >> + > >> + movl PER_CPU_VAR(cpu_current_top_of_stack), %esi > >> + leal -TOP_OF_KERNEL_STACK_PADDING-PTREGS_SIZE(%esi), %esp > >> + > >> + call do_exit > >> +1: jmp 1b > >> +END(rewind_stack_do_exit) > >> diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S > >> index 9ee0da1807ed..b846875aeea6 100644 > >> --- a/arch/x86/entry/entry_64.S > >> +++ b/arch/x86/entry/entry_64.S > >> @@ -1423,3 +1423,14 @@ ENTRY(ignore_sysret) > >> mov $-ENOSYS, %eax > >> sysret > >> END(ignore_sysret) > >> + > >> +ENTRY(rewind_stack_do_exit) > >> + /* Prevent any naive code from trying to unwind to our caller. */ > >> + xorl %ebp, %ebp > > > > s/ebp/rbp/g/ ? > > No, this quirk of the x86-64 instruction set will zero-extend to > 64-bits without needing a REX prefix. Ah, so it makes the instruction smaller. And I see that gcc also does the same. In that case: Reviewed-by: Josh Poimboeuf <jpoimboe@xxxxxxxxxx> -- Josh -- To unsubscribe from this list: send the line "unsubscribe linux-arch" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
