From 9d8ad5d6c7fce31fd2c0fd4fe9977bda3e92e340 Mon Sep 17 00:00:00 2001 From: Vegard Nossum Date: Fri, 27 Jun 2008 17:22:17 +0200 Subject: [PATCH] x86: don't destroy %rbp on kernel-mode faults From the code: "B stepping K8s sometimes report an truncated RIP for IRET exceptions returning to compat mode. Check for these here too." The code then proceeds to truncate the upper 32 bits of %rbp. This means that when do_page_fault() is finally called, its prologue, do_page_fault: push %rbp movl %rsp, %rbp will put the truncated base pointer on the stack. This means that the stack tracer will not be able to follow the base-pointer changes and will see all subsequent stack frames as unreliable. This patch changes the code to use a different register (%rcx) for the checking and leaves %rbp untouched. Signed-off-by: Vegard Nossum Signed-off-by: Pekka Enberg Acked-by: Arjan van de Ven Cc: Andi Kleen Cc: Pekka Enberg Signed-off-by: Ingo Molnar --- arch/x86/kernel/entry_64.S | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S index 556a8df522a..fa1c9eb7f60 100644 --- a/arch/x86/kernel/entry_64.S +++ b/arch/x86/kernel/entry_64.S @@ -926,11 +926,11 @@ error_kernelspace: iret run with kernel gs again, so don't set the user space flag. B stepping K8s sometimes report an truncated RIP for IRET exceptions returning to compat mode. Check for these here too. */ - leaq irq_return(%rip),%rbp - cmpq %rbp,RIP(%rsp) + leaq irq_return(%rip),%rcx + cmpq %rcx,RIP(%rsp) je error_swapgs - movl %ebp,%ebp /* zero extend */ - cmpq %rbp,RIP(%rsp) + movl %ecx,%ecx /* zero extend */ + cmpq %rcx,RIP(%rsp) je error_swapgs cmpq $gs_change,RIP(%rsp) je error_swapgs -- 2.41.1