On Thu, 14 Sep 2023 16:08:33 +0800 Haibo Li <haibo.li@xxxxxxxxxxxx> wrote:
> when the input address is illegal,the corresponding shadow address
> from kasan_mem_to_shadow may have no mapping in mmu table.
> Access such shadow address causes kernel oops.
> Here is a sample about oops on arm64(VA 39bit) with KASAN_SW_TAGS on:
>
> [ffffffb80aaaaaaa] pgd=000000005d3ce003, p4d=000000005d3ce003,
> pud=000000005d3ce003, pmd=0000000000000000
> Internal error: Oops: 0000000096000006 [#1] PREEMPT SMP
> Modules linked in:
> CPU: 3 PID: 100 Comm: sh Not tainted 6.6.0-rc1-dirty #43
> Hardware name: linux,dummy-virt (DT)
> pstate: 80000005 (Nzcv daif -PAN -UAO -TCO -DIT -SSBS BTYPE=--)
> pc : __hwasan_load8_noabort+0x5c/0x90
> lr : do_ib_ob+0xf4/0x110
> ffffffb80aaaaaaa is the shadow address for efffff80aaaaaaaa.
> The problem is reading invalid shadow in kasan_check_range.
>
> The generic kasan also has similar oops.
>
> To fix it,check shadow address by reading it with no fault.
>
> After this patch,KASAN is able to report invalid memory access
> for this case.
>
Thanks.
> --- a/mm/kasan/kasan.h
> +++ b/mm/kasan/kasan.h
> @@ -304,8 +304,17 @@ static __always_inline bool addr_has_metadata(const void *addr)
> #ifdef __HAVE_ARCH_SHADOW_MAP
> return (kasan_mem_to_shadow((void *)addr) != NULL);
> #else
> - return (kasan_reset_tag(addr) >=
> - kasan_shadow_to_mem((void *)KASAN_SHADOW_START));
> + u8 *shadow, shadow_val;
> +
> + if (kasan_reset_tag(addr) <
> + kasan_shadow_to_mem((void *)KASAN_SHADOW_START))
> + return false;
> + /* use read with nofault to check whether the shadow is accessible */
> + shadow = kasan_mem_to_shadow((void *)addr);
> + __get_kernel_nofault(&shadow_val, shadow, u8, fault);
> + return true;
> +fault:
> + return false;
> #endif
> }
Are we able to identify a Fixes: target for this?
9d7b7dd946924de43021f57a8bee122ff0744d93 ("kasan: split out
print_report from __kasan_report") altered the code but I expect the
bug was present before that commit.
Seems this bug has been there for over a year. Can you suggest why it
has been discovered after such a lengthy time?
