On Thu, Jun 16, 2016 at 10:50 AM, Josh Poimboeuf <jpoim...@redhat.com> wrote: > On Wed, Jun 15, 2016 at 05:28:30PM -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 <l...@kernel.org> >> --- >> 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..1499db695a88 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-PT_OLDSS(%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..394cad73e890 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 >> + >> + movq PER_CPU_VAR(cpu_current_top_of_stack), %rax >> + leaq -TOP_OF_KERNEL_STACK_PADDING-SS(%rax), %rsp > > I think this should be: > > leaq -TOP_OF_KERNEL_STACK_PADDING-SIZEOF_PTREGS, %rsp > > That way when it calls do_exit(), the stack frame will be placed at the > conventional spot where a smart unwinder would expect to find it.
Whoops! --Andy
