[v3,2/2] kasan, arm64: fix pointer tags in KASAN reports
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Message ID ff30b0afe6005fd046f9ac72bfb71822aedccd89.1610731872.git.andreyknvl@google.com
State In Next
Commit c5db16918b1b8eca1512de6698faf8d9e265470f
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Series
  • kasan: fixes for 5.11-rc
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Commit Message

Andrey Konovalov Jan. 15, 2021, 5:41 p.m. UTC
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 <andreyknvl@google.com>
---
 arch/arm64/mm/fault.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

Comments

Catalin Marinas Jan. 15, 2021, 5:59 p.m. UTC | #1
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 <catalin.marinas@arm.com>

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).
Vincenzo Frascino Jan. 15, 2021, 6:03 p.m. UTC | #2
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 <andreyknvl@google.com>

Reviewed-by: Vincenzo Frascino <vincenzo.frascino@arm.com>

> ---
>  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;
>  }
>
Andrey Konovalov Jan. 15, 2021, 6:08 p.m. UTC | #3
On Fri, Jan 15, 2021 at 6:59 PM Catalin Marinas <catalin.marinas@arm.com> 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 <catalin.marinas@arm.com>
>
> 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!

Patch
diff mbox series

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;
 }