From 2deb4be28077638591fe5fc593b7f8aabc140f42 Mon Sep 17 00:00:00 2001 From: Andy Lutomirski Date: Thu, 14 Jul 2016 13:22:55 -0700 Subject: [PATCH] x86/dumpstack: When OOPSing, rewind the stack before do_exit() 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. Signed-off-by: Andy Lutomirski Reviewed-by: Josh Poimboeuf Cc: Borislav Petkov Cc: Brian Gerst Cc: Denys Vlasenko Cc: H. Peter Anvin Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Thomas Gleixner Link: http://lkml.kernel.org/r/32f73ceb372ec61889598da5e5b145889b9f2e19.1468527351.git.luto@kernel.org Signed-off-by: Ingo Molnar --- arch/x86/entry/entry_32.S | 11 +++++++++++ arch/x86/entry/entry_64.S | 11 +++++++++++ arch/x86/kernel/dumpstack.c | 10 +++++++++- 3 files changed, 31 insertions(+), 1 deletion(-) 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 + + movq PER_CPU_VAR(cpu_current_top_of_stack), %rax + leaq -TOP_OF_KERNEL_STACK_PADDING-PTREGS_SIZE(%rax), %rsp + + call do_exit +1: jmp 1b +END(rewind_stack_do_exit) diff --git a/arch/x86/kernel/dumpstack.c b/arch/x86/kernel/dumpstack.c index cc88e25d73e9..de8242d8bb61 100644 --- a/arch/x86/kernel/dumpstack.c +++ b/arch/x86/kernel/dumpstack.c @@ -234,6 +234,8 @@ unsigned long oops_begin(void) EXPORT_SYMBOL_GPL(oops_begin); NOKPROBE_SYMBOL(oops_begin); +void __noreturn rewind_stack_do_exit(int signr); + void oops_end(unsigned long flags, struct pt_regs *regs, int signr) { if (regs && kexec_should_crash(current)) @@ -255,7 +257,13 @@ void oops_end(unsigned long flags, struct pt_regs *regs, int signr) panic("Fatal exception in interrupt"); if (panic_on_oops) panic("Fatal exception"); - do_exit(signr); + + /* + * We're not going to return, but we might be on an IST stack or + * have very little stack space left. Rewind the stack and kill + * the task. + */ + rewind_stack_do_exit(signr); } NOKPROBE_SYMBOL(oops_end); -- 2.20.1