Re: BISECTED: 'alloc_tag: populate memory for module tags as needed' crashes on boot.

[Ben Greear <greearb@candelatech.com>]

On 12/6/24 14:03, Suren Baghdasaryan wrote:
> On Fri, Dec 6, 2024 at 1:50 PM Ben Greear <greearb@candelatech.com> wrote:
>>
>> Hello Suren,
>>
>> My system crashes on bootup, and I bisected to this commit.
>>
>> 0f9b685626daa2f8e19a9788625c9b624c223e45 is the first bad commit
>> commit 0f9b685626daa2f8e19a9788625c9b624c223e45
>> Author: Suren Baghdasaryan <surenb@google.com>
>> Date:   Wed Oct 23 10:07:57 2024 -0700
>>
>>       alloc_tag: populate memory for module tags as needed
>>
>>       The memory reserved for module tags does not need to be backed by physical
>>       pages until there are tags to store there.  Change the way we reserve this
>>       memory to allocate only virtual area for the tags and populate it with
>>       physical pages as needed when we load a module.
>>
>> The crash looks like this:
>>
>> BUG: unable to handle page fault for address: fffffbfff4041000
>> #PF: supervisor read access in kernel mode
>> #PF: error_code(0x0000) - not-present page
>> PGD 44d0e7067 P4D 44d0e7067 PUD 44d0e3067 PMD 10bb38067 PTE 0
>> Oops: Oops: 0000 [#1] PREEMPT SMP KASAN
>> CPU: 0 UID: 0 PID: 319 Comm: systemd-udevd Not tainted 6.12.0-rc6+ #21
>> Hardware name: Default string Default string/SKYBAY, BIOS 5.12 02/15/2023
>> RIP: 0010:kasan_check_range+0xa5/0x190
>> Code: 8d 5a 07 4c 0f 49 da 49 c1 fb 03 45 85 db 0f 84 ce 00 00 00 45 89 db 4a 8d 14 d8 eb 0d 48 83 c0 08 48 39 d0 0f 84 b29
>> RSP: 0018:ffff88812c26f980 EFLAGS: 00010206
>> RAX: fffffbfff4041000 RBX: fffffbfff404101e RCX: ffffffff814ec29b
>> [  OK  DX: fffffbfff4041018 RSI: 00000000000000f0 RDI: ffffffffa0208000
>> 0m] Finished BP: fffffbfff4041000 R08: 0000000000000001 R09: fffffbfff404101d
>> ;1;39msystemd-udR10: ffffffffa02080ef R11: 0000000000000003 R12: ffffffffa0208000
>> ev-trig…e R13: ffffc90000dac7c8 R14: ffffc90000dac7e8 R15: dffffc0000000000
>> - Coldplug All uFS:  00007fe869216b40(0000) GS:ffff88841da00000(0000) knlGS:0000000000000000
>> dev Devices.
>> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>> CR2: fffffbfff4041000 CR3: 0000000121e86002 CR4: 00000000003706f0
>> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
>> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
>> Call Trace:
>>    <TASK>
>> [  OK  ? __die+0x1f/0x60
>> 0m] Reached targ ? page_fault_oops+0x258/0x910
>> et sysi ? dump_pagetable+0x690/0x690
>> nit.target - ? search_bpf_extables+0x22/0x250
>>    System Initiali ? trace_page_fault_kernel+0x120/0x120
>> zation.
>>    ? search_bpf_extables+0x164/0x250
>>    ? kasan_check_range+0xa5/0x190
>>    ? fixup_exception+0x4d/0xc70
>>    ? exc_page_fault+0xe1/0xf0
>> [  OK  ? asm_exc_page_fault+0x22/0x30
>> 0m] Reached targ ? load_module+0x3d7b/0x7560
>> et netw ? kasan_check_range+0xa5/0x190
>> ork.target - __asan_memcpy+0x38/0x60
>>    Network.
>>    load_module+0x3d7b/0x7560
>>    ? module_frob_arch_sections+0x30/0x30
>>    ? lockdep_lock+0xbe/0x1b0
>>    ? rw_verify_area+0x18d/0x5e0
>>    ? kernel_read_file+0x246/0x870
>>    ? __x64_sys_fspick+0x290/0x290
>>    ? init_module_from_file+0xd1/0x130
>>    init_module_from_file+0xd1/0x130
>>    ? __ia32_sys_init_module+0xa0/0xa0
>>    ? lock_acquire+0x2d/0xb0
>>    ? idempotent_init_module+0x116/0x790
>>    ? do_raw_spin_unlock+0x54/0x220
>>    idempotent_init_module+0x226/0x790
>>    ? init_module_from_file+0x130/0x130
>>    ? vm_mmap_pgoff+0x203/0x2e0
>>    __x64_sys_finit_module+0xba/0x130
>>    do_syscall_64+0x69/0x160
>>    entry_SYSCALL_64_after_hwframe+0x4b/0x53
>> RIP: 0033:0x7fe869de327d
>> Code: 5d c3 66 2e 0f 1f 84 00 00 00 00 00 90 f3 0f 1e fa 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 248
>> RSP: 002b:00007ffe34a828d8 EFLAGS: 00000246 ORIG_RAX: 0000000000000139
>> RAX: ffffffffffffffda RBX: 0000557fa8f3f3f0 RCX: 00007fe869de327d
>> RDX: 0000000000000000 RSI: 00007fe869f4943c RDI: 0000000000000006
>> RBP: 00007fe869f4943c R08: 0000000000000000 R09: 0000000000000000
>> R10: 0000000000000006 R11: 0000000000000246 R12: 0000000000020000
>> R13: 0000557fa8f3f030 R14: 0000000000000000 R15: 0000557fa8f3d110
>>    </TASK>
>> Modules linked in:
>> CR2: fffffbfff4041000
>> ---[ end trace 0000000000000000 ]---
>>
>> I suspect you only hit this with an unlucky amount of debugging enabled.  The kernel config I used
>> is found here:
>>
>> http://www.candelatech.com/downloads/cfg-kasan-crash-regression.config
>>
>> I will be happy to test fixes.
> 
> Hi Ben,
> Thanks for reporting the issue. Do you have these recent fixes in your tree:
> 
> https://lore.kernel.org/all/20241130001423.1114965-1-surenb@google.com/
> https://lore.kernel.org/all/20241205170528.81000-1-hao.ge@linux.dev/
> 
> If not, couple you please apply them and see if the issue is still happening?
> Thanks,
> Suren.

Hello Suren,

Thanks for the quick response.  The first patch is already in latest Linus tree,
and I applied the second one manually.  The kernel still crashes:

(gdb) l *(load_module+0x3c46)
0xffffffff814f30d6 is in load_module (/home/greearb/git/linux-2.6/kernel/module/main.c:2624).
2619				if (i == info->index.mod &&
2620				   (WARN_ON_ONCE(shdr->sh_size != sizeof(struct module)))) {
2621					ret = -ENOEXEC;
2622					goto out_err;
2623				}
2624				memcpy(dest, (void *)shdr->sh_addr, shdr->sh_size);
2625			}
2626			/*
2627			 * Update the userspace copy's ELF section address to point to
2628			 * our newly allocated memory as a pure convenience so that
(gdb)

(gdb) l *(__asan_memcpy+0x38)
0xffffffff81b39268 is in __asan_memcpy (/home/greearb/git/linux-2.6/mm/kasan/shadow.c:105).
100	EXPORT_SYMBOL(__asan_memmove);
101	#endif
102	
103	void *__asan_memcpy(void *dest, const void *src, ssize_t len)
104	{
105		if (!kasan_check_range(src, len, false, _RET_IP_) ||
106		    !kasan_check_range(dest, len, true, _RET_IP_))
107			return NULL;
108	
109		return __memcpy(dest, src, len);
(gdb)

(gdb) l *(kasan_check_range+0xa5)
0xffffffff81b386f5 is in kasan_check_range (/home/greearb/git/linux-2.6/mm/kasan/generic.c:116).
111			start += prefix;
112		}
113	
114		words = (end - start) / 8;
115		while (words) {
116			if (unlikely(*(u64 *)start))
117				return bytes_is_nonzero(start, 8);
118			start += 8;
119			words--;
120		}
(gdb)


BUG: unable to handle page fault for address: fffffbfff4041000
#PF: supervisor read access in kernel mode
#PF: error_code(0x0000) - not-present page
PGD 44d0e7067 P4D 44d0e7067 PUD 44d0e3067 PMD 10bb3d067 PTE 0
Oops: Oops: 0000 [#1] PREEMPT SMP KASAN
CPU: 7 UID: 0 PID: 319 Comm: systemd-udevd Not tainted 6.13.0-rc1+ #24
Hardware name: Default string Default string/SKYBAY, BIOS 5.12 02/15/2023
RIP: 0010:kasan_check_range+0xa5/0x190
Code: 8d 5a 07 4c 0f 49 da 49 c1 fb 03 45 85 db 0f 84 ce 00 00 00 45 89 db 4a 8d 14 d8 eb 0d 48 83 c0 08 48 39 d0 0f 84 b29
RSP: 0018:ffff88812d3ef980 EFLAGS: 00010206
RAX: fffffbfff4041000 RBX: fffffbfff404101e RCX: ffffffff814f30d6
RDX: fffffbfff4041018 RSI: 00000000000000f0 RDI: ffffffffa0208000
[  OK  BP: fffffbfff4041000 R08: 0000000000000001 R09: fffffbfff404101d
0m] Finished 10: ffffffffa02080ef R11: 0000000000000003 R12: ffffffffa0208000
;1;39msystemd-udR13: ffffc90000dac930 R14: ffffc90000dac950 R15: dffffc0000000000
ev-trig…e FS:  00007fc25423bb40(0000) GS:ffff88841dd80000(0000) knlGS:0000000000000000
- Coldplug All uCS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: fffffbfff4041000 CR3: 0000000128ef4003 CR4: 00000000003706f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
  <TASK>
  ? __die+0x1f/0x60
  ? page_fault_oops+0x258/0x910
  ? dump_pagetable+0x690/0x690
  ? search_bpf_extables+0x22/0x250
  ? show_ldttss+0x230/0x230
  ? search_bpf_extables+0x164/0x250
  ? kasan_check_range+0xa5/0x190
  ? fixup_exception+0x4d/0xc70
  ? exc_page_fault+0xe1/0xf0
  ? asm_exc_page_fault+0x22/0x30
  ? load_module+0x3c46/0x8680
  ? kasan_check_range+0xa5/0x190
  __asan_memcpy+0x38/0x60
  load_module+0x3c46/0x8680
  ? __kernel_read+0x270/0x9f0
  ? module_frob_arch_sections+0x30/0x30
  ? lockdep_lock+0xbe/0x1b0
  ? rw_verify_area+0x18d/0x5e0
  ? kernel_read_file+0x246/0x870
  ? __x64_sys_fspick+0x290/0x290
  ? init_module_from_file+0xd1/0x130
  init_module_from_file+0xd1/0x130
  ? __ia32_sys_init_module+0xa0/0xa0
  ? lock_acquire+0x2d/0xb0
  ? idempotent_init_module+0x10d/0x780
  ? do_raw_spin_unlock+0x54/0x220
  idempotent_init_module+0x21d/0x780
  ? init_module_from_file+0x130/0x130
  ? __fget_files+0x1a5/0x2d0
  __x64_sys_finit_module+0xbe/0x130
  do_syscall_64+0x69/0x160
  entry_SYSCALL_64_after_hwframe+0x4b/0x53
RIP: 0033:0x7fc254e0827d
Code: 5d c3 66 2e 0f 1f 84 00 00 00 00 00 90 f3 0f 1e fa 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 248
RSP: 002b:00007ffe1750a718 EFLAGS: 00000246 ORIG_RAX: 0000000000000139
RAX: ffffffffffffffda RBX: 000055da274c5500 RCX: 00007fc254e0827d
RDX: 0000000000000000 RSI: 00007fc254f6e43c RDI: 0000000000000006
RBP: 00007fc254f6e43c R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000006 R11: 0000000000000246 R12: 0000000000020000
R13: 000055da2749cbb0 R14: 0000000000000000 R15: 000055da274c44a0
  </TASK>
Modules linked in:
CR2: fffffbfff4041000
---[ end trace 0000000000000000 ]---

Thanks,
Ben

-- 
Ben Greear <greearb@candelatech.com>
Candela Technologies Inc  http://www.candelatech.com