Re: [patch] x86/crash: fix crash_setup_memmap_entries() out-of-bounds access

[DaveYoung <dyoung@redhat.com>]

On 04/19/21 at 10:52am, Borislav Petkov wrote:
> Here's an attempt to explain what this fixes:
> 
> ---
> From: Mike Galbraith <efault@gmx.de>
> Date: Fri, 16 Apr 2021 14:02:07 +0200
> Subject: [PATCH] x86/crash: Fix crash_setup_memmap_entries() out-of-bounds
>  access
> 
> Commit in Fixes: added support for kexec-ing a kernel on panic using a
> new system call. As part of it, it does prepare a memory map for the new
> kernel.
> 
> However, while doing so, it wrongly accesses memory it has not
> allocated: it accesses the first element of the cmem->ranges[] array in
> memmap_exclude_ranges() but it has not allocated the memory for it in
> crash_setup_memmap_entries(). As KASAN reports:
> 
>   BUG: KASAN: vmalloc-out-of-bounds in crash_setup_memmap_entries+0x17e/0x3a0
>   Write of size 8 at addr ffffc90000426008 by task kexec/1187
> 
>   (gdb) list *crash_setup_memmap_entries+0x17e
>   0xffffffff8107cafe is in crash_setup_memmap_entries (arch/x86/kernel/crash.c:322).
>   317                                      unsigned long long mend)
>   318     {
>   319             unsigned long start, end;
>   320
>   321             cmem->ranges[0].start = mstart;
>   322             cmem->ranges[0].end = mend;
>   323             cmem->nr_ranges = 1;
>   324
>   325             /* Exclude elf header region */
>   326             start = image->arch.elf_load_addr;
>   (gdb)
> 
> Make sure the ranges array becomes a single element allocated.
> 
>  [ bp: Write a proper commit message. ]

Reviewed-by: Dave Young <dyoung@redhat.com>

> 
> Fixes: dd5f726076cc ("kexec: support for kexec on panic using new system call")
> Signed-off-by: Mike Galbraith <efault@gmx.de>
> Signed-off-by: Borislav Petkov <bp@suse.de>
> Link: https://lkml.kernel.org/r/725fa3dc1da2737f0f6188a1a9701bead257ea9d.camel@gmx.de
> ---
>  arch/x86/kernel/crash.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kernel/crash.c b/arch/x86/kernel/crash.c
> index a8f3af257e26..b1deacbeb266 100644
> --- a/arch/x86/kernel/crash.c
> +++ b/arch/x86/kernel/crash.c
> @@ -337,7 +337,7 @@ int crash_setup_memmap_entries(struct kimage *image, struct boot_params *params)
>  	struct crash_memmap_data cmd;
>  	struct crash_mem *cmem;
>  
> -	cmem = vzalloc(sizeof(struct crash_mem));
> +	cmem = vzalloc(struct_size(cmem, ranges, 1));
>  	if (!cmem)
>  		return -ENOMEM;
>  
> -- 
> 2.29.2
> 
> -- 
> Regards/Gruss,
>     Boris.
> 
> https://people.kernel.org/tglx/notes-about-netiquette
> 

Thanks
Dave