On 1/15/21 5:41 PM, Andrey Konovalov wrote:
> As of the "arm64: expose FAR_EL1 tag bits in siginfo" patch, the address
> that is passed to report_tag_fault has pointer tags in the format of 0x0X,
> while KASAN uses 0xFX format (note the difference in the top 4 bits).
>
> Fix up the pointer tag for kernel pointers in do_tag_check_fault by
> setting them to the same value as bit 55. Explicitly use __untagged_addr()
> instead of untagged_addr(), as the latter doesn't affect TTBR1 addresses.
>
> Link:
> https://linux-review.googlesource.com/id/I9ced973866036d8679e8f4ae325de547eb969649
> Fixes: dceec3ff7807 ("arm64: expose FAR_EL1 tag bits in siginfo")
> Fixes: 4291e9ee6189 ("kasan, arm64: print report from tag fault handler")
> Signed-off-by: Andrey Konovalov <[email protected]>
Reviewed-by: Vincenzo Frascino <[email protected]>
> ---
> arch/arm64/mm/fault.c | 7 ++++---
> 1 file changed, 4 insertions(+), 3 deletions(-)
>
> diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
> index 3c40da479899..35d75c60e2b8 100644
> --- a/arch/arm64/mm/fault.c
> +++ b/arch/arm64/mm/fault.c
> @@ -709,10 +709,11 @@ static int do_tag_check_fault(unsigned long far,
> unsigned int esr,
> struct pt_regs *regs)
> {
> /*
> - * The architecture specifies that bits 63:60 of FAR_EL1 are UNKNOWN
> for tag
> - * check faults. Mask them out now so that userspace doesn't see them.
> + * The architecture specifies that bits 63:60 of FAR_EL1 are UNKNOWN
> + * for tag check faults. Set them to corresponding bits in the untagged
> + * address.
> */
> - far &= (1UL << 60) - 1;
> + far = (__untagged_addr(far) & ~MTE_TAG_MASK) | (far & MTE_TAG_MASK);
> do_bad_area(far, esr, regs);
> return 0;
> }
>
--
Regards,
Vincenzo
