linux-kernel - Re: [PATCH v4] x86/kexec: fix potential cmem->ranges out of bounds

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Message-ID: <4de3c2onosr7negqnfhekm4cpbklzmsimgdfv33c52dktqpza5@z5pb34ghz4at>
Date: Thu, 8 May 2025 12:25:15 +0800
From: Coiby Xu <coxu@...hat.com>
To: Baoquan He <bhe@...hat.com>, akpm@...ux-foundation.org
Cc: fuqiang wang <fuqiang.wang@...ystack.cn>, 
	Vivek Goyal <vgoyal@...hat.com>, Dave Young <dyoung@...hat.com>, kexec@...ts.infradead.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4] x86/kexec: fix potential cmem->ranges out of bounds

On Tue, Jan 09, 2024 at 11:46:15AM +0800, Baoquan He wrote:
>On 01/08/24 at 09:06pm, fuqiang wang wrote:
>> In memmap_exclude_ranges(), elfheader will be excluded from crashk_res.
>> In the current x86 architecture code, the elfheader is always allocated
>> at crashk_res.start. It seems that there won't be a new split range.
>> But it depends on the allocation position of elfheader in crashk_res. To
>> avoid potential out of bounds in future, add a extra slot.
>>
>> The similar issue also exists in fill_up_crash_elf_data(). The range to
>> be excluded is [0, 1M], start (0) is special and will not appear in the
>> middle of existing cmem->ranges[]. But in cast the low 1M could be
>> changed in the future, add a extra slot too.
>>
>> Previously discussed link:
>> [1] https://lore.kernel.org/kexec/ZXk2oBf%2FT1Ul6o0c@MiWiFi-R3L-srv/
>> [2] https://lore.kernel.org/kexec/273284e8-7680-4f5f-8065-c5d780987e59@easystack.cn/
>> [3] https://lore.kernel.org/kexec/ZYQ6O%2F57sHAPxTHm@MiWiFi-R3L-srv/
>>
>> Signed-off-by: fuqiang wang <fuqiang.wang@...ystack.cn>
>> ---
>>  arch/x86/kernel/crash.c | 21 +++++++++++++++++++--
>>  1 file changed, 19 insertions(+), 2 deletions(-)
>>
>> diff --git a/arch/x86/kernel/crash.c b/arch/x86/kernel/crash.c
>> index b6b044356f1b..d21592ad8952 100644
>> --- a/arch/x86/kernel/crash.c
>> +++ b/arch/x86/kernel/crash.c
>> @@ -149,8 +149,18 @@ static struct crash_mem *fill_up_crash_elf_data(void)
>>  	/*
>>  	 * Exclusion of crash region and/or crashk_low_res may cause
>>  	 * another range split. So add extra two slots here.
>> +	 *
>> +	 * Exclusion of low 1M may not cause another range split, because the
>> +	 * range of exclude is [0, 1M] and the condition for splitting a new
>> +	 * region is that the start, end parameters are both in a certain
>> +	 * existing region in cmem and cannot be equal to existing region's
>> +	 * start or end. Obviously, the start of [0, 1M] cannot meet this
>> +	 * condition.
>> +	 *
>> +	 * But in order to lest the low 1M could be changed in the future,
>> +	 * (e.g. [stare, 1M]), add a extra slot.
>>  	 */
>> -	nr_ranges += 2;
>> +	nr_ranges += 3;
>>  	cmem = vzalloc(struct_size(cmem, ranges, nr_ranges));
>>  	if (!cmem)
>>  		return NULL;
>> @@ -282,9 +292,16 @@ int crash_setup_memmap_entries(struct kimage *image, struct boot_params *params)
>>  	struct crash_memmap_data cmd;
>>  	struct crash_mem *cmem;
>>
>> -	cmem = vzalloc(struct_size(cmem, ranges, 1));
>> +	/*
>> +	 * In the current x86 architecture code, the elfheader is always
>> +	 * allocated at crashk_res.start. But it depends on the allocation
>> +	 * position of elfheader in crashk_res. To avoid potential out of
>> +	 * bounds in future, add a extra slot.
>> +	 */
>> +	cmem = vzalloc(struct_size(cmem, ranges, 2));
>>  	if (!cmem)
>>  		return -ENOMEM;
>> +	cmem->max_nr_ranges = 2;
>
>LGTM, thx
>
>Acked-by: Baoquan He <bhe@...hat.com>

Hi Andrew,

It seems this patch was missed. Will you pick it up? Without this patch,
kdump kernel will fail to be loaded by the kexec_file_load,

  [  139.736948] UBSAN: array-index-out-of-bounds in arch/x86/kernel/crash.c:350:25
  [  139.742360] index 0 is out of range for type 'range [*]'
  [  139.745695] CPU: 0 UID: 0 PID: 5778 Comm: kexec Not tainted 6.15.0-0.rc3.20250425git02ddfb981de8.32.fc43.x86_64 #1 PREEMPT(lazy) 
  [  139.745698] Hardware name: Amazon EC2 c5.large/, BIOS 1.0 10/16/2017
  [  139.745699] Call Trace:
  [  139.745700]  <TASK>
  [  139.745701]  dump_stack_lvl+0x5d/0x80
  [  139.745706]  ubsan_epilogue+0x5/0x2b
  [  139.745709]  __ubsan_handle_out_of_bounds.cold+0x54/0x59
  [  139.745711]  crash_setup_memmap_entries+0x2d9/0x330
  [  139.745716]  setup_boot_parameters+0xf8/0x6a0
  [  139.745720]  bzImage64_load+0x41b/0x4e0
  [  139.745722]  ? find_next_iomem_res+0x109/0x140
  [  139.745727]  ? locate_mem_hole_callback+0x109/0x170
  [  139.745737]  kimage_file_alloc_init+0x1ef/0x3e0
  [  139.745740]  __do_sys_kexec_file_load+0x180/0x2f0
  [  139.745742]  do_syscall_64+0x7b/0x160
  [  139.745745]  ? do_user_addr_fault+0x21a/0x690
  [  139.745747]  ? exc_page_fault+0x7e/0x1a0
  [  139.745749]  entry_SYSCALL_64_after_hwframe+0x76/0x7e
  [  139.745751] RIP: 0033:0x7f7712c84e4d

Thanks!

-- 
Best regards,
Coiby