lkml.org 
[lkml]   [2017]   [Jun]   [21]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: [criu] 1M guard page ruined restore
From
Date
On 06/21/2017 08:01 PM, Oleg Nesterov wrote:
> On 06/21, Cyrill Gorcunov wrote:
>>
>> On Wed, Jun 21, 2017 at 05:57:30PM +0200, Oleg Nesterov wrote:
>>>>
>>>> p = fake_grow_down;
>>>> *p-- = 'c';
>>>
>>> I guess this works? I mean, *p-- = 'c' should not fail...
>>
>> It fails.
>
> Hmm. Impossible ;) could you add the additional printf's to re-check?
>
>> Here is the complete code. It supposed to _extend_ stack but it fails
>> on the latest master + Hugh's [PATCH] mm: fix new crash in unmapped_area_topdown()
>> ---
>> [root@fc2 criu]# ~/st2
>> start_addr 7fe6162a8000
>> start_addr 7fe6163d9000
>> Segmentation fault (core dumped)
>> ---
>> #include <stdio.h>
>> #include <stdlib.h>
>> #include <errno.h>
>> #include <stdlib.h>
>> #include <string.h>
>> #include <unistd.h>
>>
>> #include <sys/mman.h>
>>
>> #define PAGE_SIZE 4096
>>
>> int main(int argc, char **argv)
>> {
>> char *start_addr, *start_addr1, *fake_grow_down, *test_addr, *grow_down;
>> volatile char *p;
>>
>> start_addr = mmap(NULL, PAGE_SIZE * 512, PROT_READ | PROT_WRITE, MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);
>> if (start_addr == MAP_FAILED) {
>> printf("Can't mal a new region");
>> return 1;
>> }
>> printf("start_addr %lx\n", start_addr);
>> munmap(start_addr, PAGE_SIZE * 512);
>>
>> start_addr += PAGE_SIZE * 300;
>>
>> fake_grow_down = mmap(start_addr + PAGE_SIZE * 5, PAGE_SIZE,
>> PROT_READ | PROT_WRITE,
>> MAP_ANONYMOUS | MAP_PRIVATE | MAP_FIXED | MAP_GROWSDOWN, -1, 0);
>> if (fake_grow_down == MAP_FAILED) {
>> printf("Can't mal a new region");
>> return 1;
>> }
>> printf("start_addr %lx\n", fake_grow_down);
>>
>> p = fake_grow_down;
>> *p-- = 'c';
>
> once again, I can't believe this STORE can fail...
>
>> *p = 'b';
>
> Ah. I forgot about another kernel "feature" ;) not related to the recent guard
> page changes...
>
> Could you test the patch below?

Well, for me only the second store caused segfault.
With your patch it passes..

>
>
> diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
> index 8ad91a0..edc5d68 100644
> --- a/arch/x86/mm/fault.c
> +++ b/arch/x86/mm/fault.c
> @@ -1416,7 +1416,7 @@ __do_page_fault(struct pt_regs *regs, unsigned long error_code,
> * and pusha to work. ("enter $65535, $31" pushes
> * 32 pointers and then decrements %sp by 65535.)
> */
> - if (unlikely(address + 65536 + 32 * sizeof(unsigned long) < regs->sp)) {
> +if (0) if (unlikely(address + 65536 + 32 * sizeof(unsigned long) < regs->sp)) {
> bad_area(regs, error_code, address);
> return;
> }
>

--
Dmitry

\
 
 \ /
  Last update: 2017-06-21 19:16    [W:0.079 / U:0.472 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site