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 before calling kasan_report.
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 | 2 ++
1 file changed, 2 insertions(+)
diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
index 3c40da479899..a218f6f2fdc8 100644
--- a/arch/arm64/mm/fault.c
+++ b/arch/arm64/mm/fault.c
@@ -304,6 +304,8 @@ static void report_tag_fault(unsigned long addr, unsigned int esr,
{
bool is_write = ((esr & ESR_ELx_WNR) >> ESR_ELx_WNR_SHIFT) != 0;
+ /* The format of KASAN tags is 0xF<x>. */
+ addr |= (0xF0UL << MTE_TAG_SHIFT);
/*
* SAS bits aren't set for all faults reported in EL1, so we can't
* find out access size.
--
2.30.0.284.gd98b1dd5eaa7-goog
On Wed, Jan 13, 2021 at 05:03:30PM +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 before calling kasan_report.
>
> 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 | 2 ++
> 1 file changed, 2 insertions(+)
>
> diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
> index 3c40da479899..a218f6f2fdc8 100644
> --- a/arch/arm64/mm/fault.c
> +++ b/arch/arm64/mm/fault.c
> @@ -304,6 +304,8 @@ static void report_tag_fault(unsigned long addr, unsigned int esr,
> {
> bool is_write = ((esr & ESR_ELx_WNR) >> ESR_ELx_WNR_SHIFT) != 0;
>
> + /* The format of KASAN tags is 0xF<x>. */
> + addr |= (0xF0UL << MTE_TAG_SHIFT);
Ah, I see, that top 4 bits are zeroed by do_tag_check_fault(). When this
was added, the only tag faults were generated for user addresses.
Anyway, I'd rather fix it in there based on bit 55, something like (only
compile-tested):
diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
index 3c40da479899..2b71079d2d32 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 the 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;
}
--
Catalin
On Wed, Jan 13, 2021 at 5:54 PM Catalin Marinas <[email protected]> wrote:
>
> On Wed, Jan 13, 2021 at 05:03:30PM +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 before calling kasan_report.
> >
> > 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 | 2 ++
> > 1 file changed, 2 insertions(+)
> >
> > diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
> > index 3c40da479899..a218f6f2fdc8 100644
> > --- a/arch/arm64/mm/fault.c
> > +++ b/arch/arm64/mm/fault.c
> > @@ -304,6 +304,8 @@ static void report_tag_fault(unsigned long addr, unsigned int esr,
> > {
> > bool is_write = ((esr & ESR_ELx_WNR) >> ESR_ELx_WNR_SHIFT) != 0;
> >
> > + /* The format of KASAN tags is 0xF<x>. */
> > + addr |= (0xF0UL << MTE_TAG_SHIFT);
>
> Ah, I see, that top 4 bits are zeroed by do_tag_check_fault(). When this
> was added, the only tag faults were generated for user addresses.
>
> Anyway, I'd rather fix it in there based on bit 55, something like (only
> compile-tested):
>
> diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
> index 3c40da479899..2b71079d2d32 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 the 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;
> }
Sounds good, will do in v3, thanks!
On Fri, Jan 15, 2021 at 02:12:24PM +0100, Andrey Konovalov wrote:
> On Wed, Jan 13, 2021 at 5:54 PM Catalin Marinas <[email protected]> wrote:
> >
> > On Wed, Jan 13, 2021 at 05:03:30PM +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 before calling kasan_report.
> > >
> > > 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 | 2 ++
> > > 1 file changed, 2 insertions(+)
> > >
> > > diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
> > > index 3c40da479899..a218f6f2fdc8 100644
> > > --- a/arch/arm64/mm/fault.c
> > > +++ b/arch/arm64/mm/fault.c
> > > @@ -304,6 +304,8 @@ static void report_tag_fault(unsigned long addr, unsigned int esr,
> > > {
> > > bool is_write = ((esr & ESR_ELx_WNR) >> ESR_ELx_WNR_SHIFT) != 0;
> > >
> > > + /* The format of KASAN tags is 0xF<x>. */
> > > + addr |= (0xF0UL << MTE_TAG_SHIFT);
> >
> > Ah, I see, that top 4 bits are zeroed by do_tag_check_fault(). When this
> > was added, the only tag faults were generated for user addresses.
> >
> > Anyway, I'd rather fix it in there based on bit 55, something like (only
> > compile-tested):
> >
> > diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
> > index 3c40da479899..2b71079d2d32 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 the 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;
> > }
>
> Sounds good, will do in v3, thanks!
I wonder if this one gives the same result (so please check):
far = u64_replace_bits(untagged_addr(far), far, MTE_TAG_MASK);
(defined in linux/bitfield.h)
--
Catalin
On Fri, Jan 15, 2021 at 4:07 PM Catalin Marinas <[email protected]> wrote:
>
> On Fri, Jan 15, 2021 at 02:12:24PM +0100, Andrey Konovalov wrote:
> > On Wed, Jan 13, 2021 at 5:54 PM Catalin Marinas <[email protected]> wrote:
> > >
> > > On Wed, Jan 13, 2021 at 05:03:30PM +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 before calling kasan_report.
> > > >
> > > > 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 | 2 ++
> > > > 1 file changed, 2 insertions(+)
> > > >
> > > > diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
> > > > index 3c40da479899..a218f6f2fdc8 100644
> > > > --- a/arch/arm64/mm/fault.c
> > > > +++ b/arch/arm64/mm/fault.c
> > > > @@ -304,6 +304,8 @@ static void report_tag_fault(unsigned long addr, unsigned int esr,
> > > > {
> > > > bool is_write = ((esr & ESR_ELx_WNR) >> ESR_ELx_WNR_SHIFT) != 0;
> > > >
> > > > + /* The format of KASAN tags is 0xF<x>. */
> > > > + addr |= (0xF0UL << MTE_TAG_SHIFT);
> > >
> > > Ah, I see, that top 4 bits are zeroed by do_tag_check_fault(). When this
> > > was added, the only tag faults were generated for user addresses.
> > >
> > > Anyway, I'd rather fix it in there based on bit 55, something like (only
> > > compile-tested):
> > >
> > > diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
> > > index 3c40da479899..2b71079d2d32 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 the 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;
> > > }
> >
> > Sounds good, will do in v3, thanks!
>
> I wonder if this one gives the same result (so please check):
>
> far = u64_replace_bits(untagged_addr(far), far, MTE_TAG_MASK);
>
> (defined in linux/bitfield.h)
No, it zeroes out the tag. Not sure why. I took a brief look at the
implementation and didn't get how it's supposed to work - too much bit
trickery.
On Wed, Jan 13, 2021 at 5:54 PM Catalin Marinas <[email protected]> wrote:
>
> On Wed, Jan 13, 2021 at 05:03:30PM +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 before calling kasan_report.
> >
> > 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 | 2 ++
> > 1 file changed, 2 insertions(+)
> >
> > diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
> > index 3c40da479899..a218f6f2fdc8 100644
> > --- a/arch/arm64/mm/fault.c
> > +++ b/arch/arm64/mm/fault.c
> > @@ -304,6 +304,8 @@ static void report_tag_fault(unsigned long addr, unsigned int esr,
> > {
> > bool is_write = ((esr & ESR_ELx_WNR) >> ESR_ELx_WNR_SHIFT) != 0;
> >
> > + /* The format of KASAN tags is 0xF<x>. */
> > + addr |= (0xF0UL << MTE_TAG_SHIFT);
>
> Ah, I see, that top 4 bits are zeroed by do_tag_check_fault(). When this
> was added, the only tag faults were generated for user addresses.
>
> Anyway, I'd rather fix it in there based on bit 55, something like (only
> compile-tested):
>
> diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
> index 3c40da479899..2b71079d2d32 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 the 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;
> }
BTW, we can do "untagged_addr(far) | (far & MTE_TAG_MASK)" here, as
untagged_addr() doesn't change kernel pointers.
On Fri, Jan 15, 2021 at 05:30:40PM +0100, Andrey Konovalov wrote:
> On Wed, Jan 13, 2021 at 5:54 PM Catalin Marinas <[email protected]> wrote:
> > On Wed, Jan 13, 2021 at 05:03:30PM +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 before calling kasan_report.
> > >
> > > 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 | 2 ++
> > > 1 file changed, 2 insertions(+)
> > >
> > > diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
> > > index 3c40da479899..a218f6f2fdc8 100644
> > > --- a/arch/arm64/mm/fault.c
> > > +++ b/arch/arm64/mm/fault.c
> > > @@ -304,6 +304,8 @@ static void report_tag_fault(unsigned long addr, unsigned int esr,
> > > {
> > > bool is_write = ((esr & ESR_ELx_WNR) >> ESR_ELx_WNR_SHIFT) != 0;
> > >
> > > + /* The format of KASAN tags is 0xF<x>. */
> > > + addr |= (0xF0UL << MTE_TAG_SHIFT);
> >
> > Ah, I see, that top 4 bits are zeroed by do_tag_check_fault(). When this
> > was added, the only tag faults were generated for user addresses.
> >
> > Anyway, I'd rather fix it in there based on bit 55, something like (only
> > compile-tested):
> >
> > diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
> > index 3c40da479899..2b71079d2d32 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 the 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;
> > }
>
> BTW, we can do "untagged_addr(far) | (far & MTE_TAG_MASK)" here, as
> untagged_addr() doesn't change kernel pointers.
untagged_addr() does change tagged kernel pointers, it sign-extends from
bit 55. So the top byte becomes 0xff and you can no longer or the tag
bits in.
--
Catalin
On Fri, Jan 15, 2021 at 5:56 PM Catalin Marinas <[email protected]> wrote:
>
> On Fri, Jan 15, 2021 at 05:30:40PM +0100, Andrey Konovalov wrote:
> > On Wed, Jan 13, 2021 at 5:54 PM Catalin Marinas <[email protected]> wrote:
> > > On Wed, Jan 13, 2021 at 05:03:30PM +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 before calling kasan_report.
> > > >
> > > > 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 | 2 ++
> > > > 1 file changed, 2 insertions(+)
> > > >
> > > > diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
> > > > index 3c40da479899..a218f6f2fdc8 100644
> > > > --- a/arch/arm64/mm/fault.c
> > > > +++ b/arch/arm64/mm/fault.c
> > > > @@ -304,6 +304,8 @@ static void report_tag_fault(unsigned long addr, unsigned int esr,
> > > > {
> > > > bool is_write = ((esr & ESR_ELx_WNR) >> ESR_ELx_WNR_SHIFT) != 0;
> > > >
> > > > + /* The format of KASAN tags is 0xF<x>. */
> > > > + addr |= (0xF0UL << MTE_TAG_SHIFT);
> > >
> > > Ah, I see, that top 4 bits are zeroed by do_tag_check_fault(). When this
> > > was added, the only tag faults were generated for user addresses.
> > >
> > > Anyway, I'd rather fix it in there based on bit 55, something like (only
> > > compile-tested):
> > >
> > > diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
> > > index 3c40da479899..2b71079d2d32 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 the 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;
> > > }
> >
> > BTW, we can do "untagged_addr(far) | (far & MTE_TAG_MASK)" here, as
> > untagged_addr() doesn't change kernel pointers.
>
> untagged_addr() does change tagged kernel pointers, it sign-extends from
> bit 55. So the top byte becomes 0xff and you can no longer or the tag
> bits in.
That's __untagged_addr(), untagged_addr() keeps the bits for kernel
pointers as of 597399d0cb91.
On Fri, Jan 15, 2021 at 06:00:36PM +0100, Andrey Konovalov wrote:
> On Fri, Jan 15, 2021 at 5:56 PM Catalin Marinas <[email protected]> wrote:
> >
> > On Fri, Jan 15, 2021 at 05:30:40PM +0100, Andrey Konovalov wrote:
> > > On Wed, Jan 13, 2021 at 5:54 PM Catalin Marinas <[email protected]> wrote:
> > > > On Wed, Jan 13, 2021 at 05:03:30PM +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 before calling kasan_report.
> > > > >
> > > > > 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 | 2 ++
> > > > > 1 file changed, 2 insertions(+)
> > > > >
> > > > > diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
> > > > > index 3c40da479899..a218f6f2fdc8 100644
> > > > > --- a/arch/arm64/mm/fault.c
> > > > > +++ b/arch/arm64/mm/fault.c
> > > > > @@ -304,6 +304,8 @@ static void report_tag_fault(unsigned long addr, unsigned int esr,
> > > > > {
> > > > > bool is_write = ((esr & ESR_ELx_WNR) >> ESR_ELx_WNR_SHIFT) != 0;
> > > > >
> > > > > + /* The format of KASAN tags is 0xF<x>. */
> > > > > + addr |= (0xF0UL << MTE_TAG_SHIFT);
> > > >
> > > > Ah, I see, that top 4 bits are zeroed by do_tag_check_fault(). When this
> > > > was added, the only tag faults were generated for user addresses.
> > > >
> > > > Anyway, I'd rather fix it in there based on bit 55, something like (only
> > > > compile-tested):
> > > >
> > > > diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
> > > > index 3c40da479899..2b71079d2d32 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 the 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;
> > > > }
> > >
> > > BTW, we can do "untagged_addr(far) | (far & MTE_TAG_MASK)" here, as
> > > untagged_addr() doesn't change kernel pointers.
> >
> > untagged_addr() does change tagged kernel pointers, it sign-extends from
> > bit 55. So the top byte becomes 0xff and you can no longer or the tag
> > bits in.
>
> That's __untagged_addr(), untagged_addr() keeps the bits for kernel
> pointers as of 597399d0cb91.
Ah, you are right. In this case I think we should use __untagged_addr()
above. Even if the tag check fault happened on a kernel address, bits
63:60 are still unknown.
--
Catalin
On Fri, Jan 15, 2021 at 6:06 PM Catalin Marinas <[email protected]> wrote:
>
> On Fri, Jan 15, 2021 at 06:00:36PM +0100, Andrey Konovalov wrote:
> > On Fri, Jan 15, 2021 at 5:56 PM Catalin Marinas <[email protected]> wrote:
> > >
> > > On Fri, Jan 15, 2021 at 05:30:40PM +0100, Andrey Konovalov wrote:
> > > > On Wed, Jan 13, 2021 at 5:54 PM Catalin Marinas <[email protected]> wrote:
> > > > > On Wed, Jan 13, 2021 at 05:03:30PM +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 before calling kasan_report.
> > > > > >
> > > > > > 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 | 2 ++
> > > > > > 1 file changed, 2 insertions(+)
> > > > > >
> > > > > > diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
> > > > > > index 3c40da479899..a218f6f2fdc8 100644
> > > > > > --- a/arch/arm64/mm/fault.c
> > > > > > +++ b/arch/arm64/mm/fault.c
> > > > > > @@ -304,6 +304,8 @@ static void report_tag_fault(unsigned long addr, unsigned int esr,
> > > > > > {
> > > > > > bool is_write = ((esr & ESR_ELx_WNR) >> ESR_ELx_WNR_SHIFT) != 0;
> > > > > >
> > > > > > + /* The format of KASAN tags is 0xF<x>. */
> > > > > > + addr |= (0xF0UL << MTE_TAG_SHIFT);
> > > > >
> > > > > Ah, I see, that top 4 bits are zeroed by do_tag_check_fault(). When this
> > > > > was added, the only tag faults were generated for user addresses.
> > > > >
> > > > > Anyway, I'd rather fix it in there based on bit 55, something like (only
> > > > > compile-tested):
> > > > >
> > > > > diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
> > > > > index 3c40da479899..2b71079d2d32 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 the 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;
> > > > > }
> > > >
> > > > BTW, we can do "untagged_addr(far) | (far & MTE_TAG_MASK)" here, as
> > > > untagged_addr() doesn't change kernel pointers.
> > >
> > > untagged_addr() does change tagged kernel pointers, it sign-extends from
> > > bit 55. So the top byte becomes 0xff and you can no longer or the tag
> > > bits in.
> >
> > That's __untagged_addr(), untagged_addr() keeps the bits for kernel
> > pointers as of 597399d0cb91.
>
> Ah, you are right. In this case I think we should use __untagged_addr()
> above. Even if the tag check fault happened on a kernel address, bits
> 63:60 are still unknown.
Yeah, I keep forgetting about [__]untagged_addr() too. Maybe we need
better names? Like untagged_addr() and untagged_addr_ttbr0()?
Anyway, I'll do the explicit calculation with __untagged_addr() in the
next version.
Thanks!