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SubjectRe: [PATCH] futex:fix robust futex alignment exception
From
Date
The test case:

#include <stdio.h>
#include <linux/futex.h>
#include <syscall.h>
#include <unistd.h>
#include <stdlib.h>

int main()
{
char *p = malloc(128);

struct robust_list_head *ro1;
struct robust_list *entry;
struct robust_list *pending;

int ret = 0;

pid_t pid = getpid();

printf("p %p pid [%d] \n", p, pid);

ro1 = p;
entry = p + 20;
pending = p + 40;

ro1->list.next = entry;
ro1->list_op_pending = pending;

entry->next = &(ro1->list);

ro1->futex_offset = 41;

*((int *)((char *)entry + 41)) = pid;

printf(" entry + offert [%p] [%d] \n", (int *)((char *)entry + 41),
*((int *)((char *)entry + 41)));

ret = syscall(SYS_set_robust_list, ro1, 12);

printf("ret = [%d]\n", ret);


return 0;
}

and we test it on arm a9 platform

Alignment trap: not handling instruction e191ef9f at [<c018cf5c>]
Unhandled fault: alignment exception (0x011) at 0x01b1218d
pgd = c3b50000
[01b1218d] *pgd=843c8831, *pte=b831d75f, *ppte=b831dc7f
Internal error: : 11 [#1] SMP ARM
Modules linked in: nfsv3 veth(O) ping(O) nand mtdblock mtd_blkdevs
nand_ecc nand_ids gmac(O) pramdisk(O) rtos_kbox_panic(O)
rtos_snapshot(O) double_cluster(O) uart_suspend(O) rsm(O)
follow_huge_pfn(O) cache_ops(O) nfsd auth_rpcgss exportfs nfs_acl nfs
lockd sunrpc oid_registry grace physmap cfi_cmdset_0002 cfi_probe
cfi_util mtd gen_probe chipreg ohci_platform ehci_platform ohci_hcd
ehci_hcd vfat fat sd_mod enable_uart_rx(O)
CPU: 1 PID: 786 Comm: set_robust_list Tainted: G W O 4.4.171 #3
Hardware name: Hisilicon A9
task: ef0045e8 task.stack: c3b68000
PC is at cmpxchg_futex_value_locked+0x48/0xac
LR is at 0x42b12190
pc : [<c018cf5c>] lr : [<42b12190>] psr: 60070213
sp : c3b69ed8 ip : fffffff2 fp : c05d9eeb
r10: ffffe000 r9 : ef0045e8 r8 : 00000000
r7 : 01b12178 r6 : 00000312 r5 : 01b1218d r4 : ef0045e8
r3 : 40000000 r2 : 00000312 r1 : 01b1218d r0 : c3b69ee0
Flags: nZCv IRQs on FIQs on Mode SVC_32 ISA ARM Segment user
Control: 1ac5387d Table: 8455004a DAC: 55555555
Process set_robust_list (pid: 786, stack limit = 0xc3b68210)
Stack: (0xc3b69ed8 to 0xc3b6a000)
9ec0: c080e2a8
c018ff44
9ee0: 01b1218d dc8ba6ab 00000000 01b12164 01b12150 ef0045e8 01b12178
01b12150
9f00: 00000000 00000029 01b12178 c01900dc 00000800 00000000 ffffe000
00000000
9f20: ffffe000 ef0045e8 c2e6dc00 ffffe000 c2e6dc00 c01077a4 00000000
000000f8
9f40: b6fa2e30 c011afd8 ef0045e8 c2e6dc00 dc8ba6ab ef0045e8 c2e6dc00
ffffe000
9f60: ffffe000 c011f370 00000000 ef00486c ef00486c dc8ba6ab c38aed20
ffffe000
9f80: b6fa2e30 c0120d44 00000000 b6fa1500 00000000 000000f8 c01077a4
c0120e14
9fa0: b6fa1500 c0107790 b6fa1500 b6fa1500 00000000 00000000 0097fadd
00000000
9fc0: b6fa1500 b6fa1500 00000000 000000f8 00000000 00000001 b6fa6120
b6fa2e30
9fe0: 00000000 be80eb98 b6e8d4c8 b6efe53c 60070210 00000000 00000000
00000000
[<c018cf5c>] (cmpxchg_futex_value_locked) from [<c018ff44>]
(handle_futex_death+0xa8/0x110)
[<c018ff44>] (handle_futex_death) from [<c01900dc>]
(exit_robust_list+0x130/0x1b4)
[<c01900dc>] (exit_robust_list) from [<c011afd8>] (mm_release+0x1c/0x13c)
[<c011afd8>] (mm_release) from [<c011f370>] (do_exit+0x240/0x9b8)
[<c011f370>] (do_exit) from [<c0120d44>] (do_group_exit+0x58/0x108)
[<c0120d44>] (do_group_exit) from [<c0120e14> (__wake_up_parent+0x0/0x18)
Code: 0c40a011 0900001a 5bf07ff5 00f091f5 (9fef91e1)


On 2019/3/18 18:48, Peter Zijlstra wrote:
> On Sun, Mar 17, 2019 at 03:36:35PM +0100, Thomas Gleixner wrote:
>> On Fri, 15 Mar 2019, Peter Zijlstra wrote:
>
>>> That is; why aren't there any alignment tests anywhere? Or am I just
>>> gone blind?
>>
>> uaddrs for the futex syscalls are checked in get_futex_key().
>
> blind it is...
>
> Thanks!
>
>

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