2021-01-15 17:45:01

by Andrey Konovalov

Subject: [PATCH v3 2/2] kasan, arm64: fix pointer tags in KASAN reports

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]>
---
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;
}
--
2.30.0.284.gd98b1dd5eaa7-goog

2021-01-15 18:01:23

by Catalin Marinas

Subject: Re: [PATCH v3 2/2] kasan, arm64: fix pointer tags in KASAN reports

On Fri, Jan 15, 2021 at 06:41:53PM +0100, 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

Reviewed-by: Catalin Marinas <[email protected]>

Unless there are other comments, I'll queue this for -rc5 through the
arm64 tree (I already finalised the arm64 for-next/fixes branch for this
week).

--
Catalin

2021-01-15 18:02:32

by Vincenzo Frascino

Subject: Re: [PATCH v3 2/2] kasan, arm64: fix pointer tags in KASAN reports

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

2021-01-15 18:12:20

by Andrey Konovalov

Subject: Re: [PATCH v3 2/2] kasan, arm64: fix pointer tags in KASAN reports

On Fri, Jan 15, 2021 at 6:59 PM Catalin Marinas <[email protected]> wrote:
>
> On Fri, Jan 15, 2021 at 06:41:53PM +0100, 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
>
> Reviewed-by: Catalin Marinas <[email protected]>
>
> Unless there are other comments, I'll queue this for -rc5 through the
> arm64 tree (I already finalised the arm64 for-next/fixes branch for this
> week).

Sounds good, thank you!