linux-kernel - Re: [PATCH v5] x86/kexec: fix potential cmem->ranges out of bounds

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Message-ID: <aBxiod8BG9gR49Hl@MiWiFi-R3L-srv>
Date: Thu, 8 May 2025 15:52:01 +0800
From: Baoquan He <bhe@...hat.com>
To: fuqiang wang <fuqiang.wang@...ystack.cn>
Cc: Vivek Goyal <vgoyal@...hat.com>, Dave Young <dyoung@...hat.com>,
	kexec@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5] x86/kexec: fix potential cmem->ranges out of bounds

On 05/08/25 at 03:38pm, Baoquan He 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. And using
> random kexec_buf for passing dm crypt keys may cause a range split too,
> add another extra slot here.

Sorry, this should be from fuqiang wang, when I edited the patch to
reply to his patch, I forgot that. Please help makes change to set
Fuqiang as the patch author, I just adapted the content based on Coiby's
patches.

> 
> 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>
> Signed-off-by: Baoquan He <bhe@...hat.com>
> ---
> v4->v5:
> - This is on top of Coiby's LUKS patchset in branch mm-nonmm-unstable of
>   akpm/mm.git. I did some adaption based on Coiby's patches.
> - [PATCH v9 0/8] Support kdump with LUKS encryption by reusing LUKS volume keys
> 
>  arch/x86/kernel/crash.c | 23 +++++++++++++++++++----
>  1 file changed, 19 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/x86/kernel/crash.c b/arch/x86/kernel/crash.c
> index bcb534688dfe..749a60ce8b7f 100644
> --- a/arch/x86/kernel/crash.c
> +++ b/arch/x86/kernel/crash.c
> @@ -165,8 +165,18 @@ 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;
> @@ -313,10 +323,15 @@ int crash_setup_memmap_entries(struct kimage *image, struct boot_params *params)
>  	struct crash_mem *cmem;
>  
>  	/*
> -	 * Using random kexec_buf for passing dm crypt keys may cause a range
> -	 * split. So use two slots here.
> +	 * 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 an extra slot.
> +	 *
> +	 * And using random kexec_buf for passing dm crypt keys may cause a
> +	 * range split too, add another extra slot here.
>  	 */
> -	nr_ranges = 2;
> +	nr_ranges = 3;
>  	cmem = vzalloc(struct_size(cmem, ranges, nr_ranges));
>  	if (!cmem)
>  		return -ENOMEM;
> -- 
> 2.41.0
>