4.8-stable review patch. If anyone has any objections, please let me know.
------------------
From: Josh Poimboeuf <jpoim...@redhat.com>
commit 72b4f6a5e903b071f2a7c4eb1418cbe4eefdc344 upstream.
On x86_32, when an interrupt happens from kernel space, SS and SP aren't
pushed and the existing stack is used. So pt_regs is effectively two
words shorter, and the previous stack pointer is normally the memory
after the shortened pt_regs, aka '®s->sp'.
But in the rare case where the interrupt hits right after the stack
pointer has been changed to point to an empty stack, like for example
when call_on_stack() is used, the address immediately after the
shortened pt_regs is no longer on the stack. In that case, instead of
'®s->sp', the previous stack pointer should be retrieved from the
beginning of the current stack page.
kernel_stack_pointer() wants to do that, but it forgets to dereference
the pointer. So instead of returning a pointer to the previous stack,
it returns a pointer to the beginning of the current stack.
Note that it's probably outside of kernel_stack_pointer()'s scope to be
switching stacks at all. The x86_64 version of this function doesn't do
it, and it would be better for the caller to do it if necessary. But
that's a patch for another day. This just fixes the original intent.
Signed-off-by: Josh Poimboeuf <jpoim...@redhat.com>
Cc: Andy Lutomirski <l...@amacapital.net>
Cc: Andy Lutomirski <l...@kernel.org>
Cc: Borislav Petkov <b...@alien8.de>
Cc: Brian Gerst <brge...@gmail.com>
Cc: Byungchul Park <byungchul.p...@lge.com>
Cc: Denys Vlasenko <dvlas...@redhat.com>
Cc: Frederic Weisbecker <fweis...@gmail.com>
Cc: H. Peter Anvin <h...@zytor.com>
Cc: Kees Cook <keesc...@chromium.org>
Cc: Linus Torvalds <torva...@linux-foundation.org>
Cc: Nilay Vaish <nilayva...@gmail.com>
Cc: Peter Zijlstra <pet...@infradead.org>
Cc: Steven Rostedt <rost...@goodmis.org>
Cc: Thomas Gleixner <t...@linutronix.de>
Fixes: 0788aa6a23cb ("x86: Prepare removal of previous_esp from i386
thread_info structure")
Link:
http://lkml.kernel.org/r/472453d6e9f6a2d4ab16aaed4935f43117111566.1471535549.git.jpoim...@redhat.com
Signed-off-by: Ingo Molnar <mi...@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>
---
arch/x86/kernel/ptrace.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
--- a/arch/x86/kernel/ptrace.c
+++ b/arch/x86/kernel/ptrace.c
@@ -173,8 +173,8 @@ unsigned long kernel_stack_pointer(struc
return sp;
prev_esp = (u32 *)(context);
- if (prev_esp)
- return (unsigned long)prev_esp;
+ if (*prev_esp)
+ return (unsigned long)*prev_esp;
return (unsigned long)regs;
}
