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

Baoquan He
2024-01-09T03:46:24Z

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@easystack.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@redhat.com>

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