The recent change fix-crash-in-entrys-restore_all.patch
childregs->esp = esp;
p->thread.esp = (unsigned long) childregs;
- p->thread.esp0 = (unsigned long) (childregs+1);
+ p->thread.esp0 = (unsigned long) (childregs+1) - 8;
p->thread.eip = (unsigned long) ret_from_fork;
introduces an inconsistency between esp and esp0 before the task is run the
first time. esp0 is no longer the actual start of the stack, but 8 bytes
off.
This shows itself clearly in a scenario when a ptracer that is set to also
ptrace eventual children traces program1 which then clones thread1. Now
the ptracer wants to modify the registers of thread1. The x86 ptrace
implementation bases it's knowledge about saved user-space registers upon
p->thread.esp0. But this will be a few bytes off causing certain writes to
the kernel stack to overwrite a saved kernel function address making the
kernel when actually running thread1 jump out into user-space. Very
spectacular.
The testcase I've used is:
/* start with strace -f ./a.out */
#include <pthread.h>
#include <stdio.h>
void *do_thread(void *p)
{
for (;;);
}
int main()
{
pthread_t one;
pthread_create(&one, NULL, &do_thread, NULL);
for (;;);
return 0;
}
So, my solution is to instead of just adjusting esp0 that creates an
inconsitent state I adjust where the user-space registers are saved with -8
bytes. This gives us the wanted extra bytes on the start of the stack and
esp0 is now correct. This solves the issues I saw from the original
testcase from Mateusz Berezecki and has survived testing here. I think
this should go into -mm a round or two first however as there might be some
cruft around depending on pt_regs lying on the start of the stack. That
however would have broken with the first change too!
It's actually a 2-line diff but I had to move the comment of why the -8 bytes
are there a few lines up. Thanks to Zwane for helping me with this.
Signed-off-by: Alexander Nyberg <alexn@telia.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
The new i386/x86_64 assemblers no longer accept instructions for moving
between a segment register and a 32bit memory location, i.e.,
movl (%eax),%ds
movl %ds,(%eax)
To generate instructions for moving between a segment register and a
16bit memory location without the 16bit operand size prefix, 0x66,
mov (%eax),%ds
mov %ds,(%eax)
should be used. It will work with both new and old assemblers. The
assembler starting from 2.16.90.0.1 will also support
movw (%eax),%ds
movw %ds,(%eax)
without the 0x66 prefix. I am enclosing patches for 2.4 and 2.6 kernels
here. The resulting kernel binaries should be unchanged as before, with
old and new assemblers, if gcc never generates memory access for
unsigned gsindex;
asm volatile("movl %%gs,%0" : "=g" (gsindex));
If gcc does generate memory access for the code above, the upper bits
in gsindex are undefined and the new assembler doesn't allow it.
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
This moves the macro loaddebug from asm-i386/suspend.h to
asm-i386/processor.h, which is the place that makes sense for it to be
defined, removes the extra copy of the same macro in
arch/i386/kernel/process.c, and makes arch/i386/kernel/signal.c use the
macro in place of its expansion.
This is a purely cosmetic cleanup for the normal i386 kernel. However, it
is handy for Xen to be able to just redefine the loaddebug macro once
instead of also changing the signal.c code.
Signed-off-by: Roland McGrath <roland@redhat.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
Fix the access-above-bottom-of-stack crash.
1. Allows to preserve the valueable optimization
2. Works for NMIs
3. Doesn't care whether or not there are more of the like instances
where the stack is left empty.
4. Seems to work for me without the crashes:)
(akpm: this is still under discussion, although I _think_ it's OK. You might
want to hold off)
Signed-off-by: Stas Sergeev <stsp@aknet.ru>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
Initial git repository build. I'm not bothering with the full history,
even though we have it. We can create a separate "historical" git
archive of that later if we want to, and in the meantime it's about
3.2GB when imported into git - space that would just make the early
git days unnecessarily complicated, when we don't have a lot of good
infrastructure for it.
Let it rip!
Alexander Nyberg