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

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Date: Tue, 9 Jan 2024 11:46:15 +0800
From: Baoquan He <bhe@...hat.com>
To: fuqiang wang <fuqiang.wang@...ystack.cn>
Cc: akpm@...ux-foundation.org, 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 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>

>  
>  	memset(&cmd, 0, sizeof(struct crash_memmap_data));
>  	cmd.params = params;
> -- 
> 2.42.0
>