ex_handler_load_unaligned_zeropad extracts the source and data register
numbers from the wrong field of the exception table.
Fixes: 753b3236
Signed-off-by: Evgenii Stepanov <[email protected]>
---
arch/arm64/mm/extable.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/arch/arm64/mm/extable.c b/arch/arm64/mm/extable.c
index c0181e60cc98..489455309695 100644
--- a/arch/arm64/mm/extable.c
+++ b/arch/arm64/mm/extable.c
@@ -40,8 +40,8 @@ static bool
ex_handler_load_unaligned_zeropad(const struct exception_table_entry *ex,
struct pt_regs *regs)
{
- int reg_data = FIELD_GET(EX_DATA_REG_DATA, ex->type);
- int reg_addr = FIELD_GET(EX_DATA_REG_ADDR, ex->type);
+ int reg_data = FIELD_GET(EX_DATA_REG_DATA, ex->data);
+ int reg_addr = FIELD_GET(EX_DATA_REG_ADDR, ex->data);
unsigned long data, addr, offset;
addr = pt_regs_read_reg(regs, reg_addr);
--
2.35.0.rc0.227.g00780c9af4-goog
On Fri, Jan 21, 2022 at 06:34:47PM -0800, Evgenii Stepanov wrote:
> ex_handler_load_unaligned_zeropad extracts the source and data register
> numbers from the wrong field of the exception table.
Could you please also include the stack dump if you get one from the
null pointer dereference?
> Fixes: 753b3236
This should be expanded:
Fixes: 753b32368705 ("arm64: extable: add load_unaligned_zeropad() handler")
Cc: <[email protected]> # 5.16.x
Thanks.
--
Catalin
On Fri, Jan 21, 2022 at 06:34:47PM -0800, Evgenii Stepanov wrote:
> ex_handler_load_unaligned_zeropad extracts the source and data register
> numbers from the wrong field of the exception table.
Ouch. Did you find this by inspection, or did this show up in testing?
Sorry about this.
I think we should be a little more explicit as to exactly what goes wrong. How
about:
| In ex_handler_load_unaligned_zeropad() we erroneously extract the data and
| addr register indices from ex->type rather than ex->data. As ex->type will
| contain EX_TYPE_LOAD_UNALIGNED_ZEROPAD (i.e. 4):
|
| * We'll always treat X0 as the address register, since EX_DATA_REG_ADDR is
| extracted from bits [9:5]. Thus, we may attempt to dereference an arbitrary
| address as X0 may hold an arbitary value.
|
| * We'll always treat X4 as the data register, since EX_DATA_REG_DATA is
| extracted from bits [4:0]. Thus we will corrupt X4 and cause arbitrary
| behaviour within load_unaligned_zeropad() and its caller.
|
| Fix this by extracting both values from ex->data as originally intended.
> Fixes: 753b3236
That should be expanded, e.g.
Fixes: 753b32368705c396 ("arm64: extable: add load_unaligned_zeropad() handler")
With those changes:
Reviewed-by: Mark Rutland <[email protected]>
Thanks,
Mark.
> Signed-off-by: Evgenii Stepanov <[email protected]>
> ---
> arch/arm64/mm/extable.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/arch/arm64/mm/extable.c b/arch/arm64/mm/extable.c
> index c0181e60cc98..489455309695 100644
> --- a/arch/arm64/mm/extable.c
> +++ b/arch/arm64/mm/extable.c
> @@ -40,8 +40,8 @@ static bool
> ex_handler_load_unaligned_zeropad(const struct exception_table_entry *ex,
> struct pt_regs *regs)
> {
> - int reg_data = FIELD_GET(EX_DATA_REG_DATA, ex->type);
> - int reg_addr = FIELD_GET(EX_DATA_REG_ADDR, ex->type);
> + int reg_data = FIELD_GET(EX_DATA_REG_DATA, ex->data);
> + int reg_addr = FIELD_GET(EX_DATA_REG_ADDR, ex->data);
> unsigned long data, addr, offset;
>
> addr = pt_regs_read_reg(regs, reg_addr);
> --
> 2.35.0.rc0.227.g00780c9af4-goog
>
On Tue, Jan 25, 2022 at 03:23:20PM +0000, Mark Rutland wrote:
> On Fri, Jan 21, 2022 at 06:34:47PM -0800, Evgenii Stepanov wrote:
> > ex_handler_load_unaligned_zeropad extracts the source and data register
> > numbers from the wrong field of the exception table.
>
> Ouch. Did you find this by inspection, or did this show up in testing?
>
> Sorry about this.
>
> I think we should be a little more explicit as to exactly what goes wrong. How
> about:
>
> | In ex_handler_load_unaligned_zeropad() we erroneously extract the data and
> | addr register indices from ex->type rather than ex->data. As ex->type will
> | contain EX_TYPE_LOAD_UNALIGNED_ZEROPAD (i.e. 4):
> |
> | * We'll always treat X0 as the address register, since EX_DATA_REG_ADDR is
> | extracted from bits [9:5]. Thus, we may attempt to dereference an arbitrary
> | address as X0 may hold an arbitary value.
> |
> | * We'll always treat X4 as the data register, since EX_DATA_REG_DATA is
> | extracted from bits [4:0]. Thus we will corrupt X4 and cause arbitrary
> | behaviour within load_unaligned_zeropad() and its caller.
> |
> | Fix this by extracting both values from ex->data as originally intended.
>
> > Fixes: 753b3236
>
> That should be expanded, e.g.
>
> Fixes: 753b32368705c396 ("arm64: extable: add load_unaligned_zeropad() handler")
>
> With those changes:
>
> Reviewed-by: Mark Rutland <[email protected]>
Looking again, sicne this isn't jsut a null-deref, can we also rework the
title, something like:
| arm64: extable: fix load_unaligned_zeropad() reg indices
Thanks,
Mark.
On Tue, Jan 25, 2022 at 7:50 AM Mark Rutland <[email protected]> wrote:
>
> On Tue, Jan 25, 2022 at 03:23:20PM +0000, Mark Rutland wrote:
> > On Fri, Jan 21, 2022 at 06:34:47PM -0800, Evgenii Stepanov wrote:
> > > ex_handler_load_unaligned_zeropad extracts the source and data register
> > > numbers from the wrong field of the exception table.
> >
> > Ouch. Did you find this by inspection, or did this show up in testing?
> >
> > Sorry about this.
> >
> > I think we should be a little more explicit as to exactly what goes wrong. How
> > about:
> >
> > | In ex_handler_load_unaligned_zeropad() we erroneously extract the data and
> > | addr register indices from ex->type rather than ex->data. As ex->type will
> > | contain EX_TYPE_LOAD_UNALIGNED_ZEROPAD (i.e. 4):
> > |
> > | * We'll always treat X0 as the address register, since EX_DATA_REG_ADDR is
> > | extracted from bits [9:5]. Thus, we may attempt to dereference an arbitrary
> > | address as X0 may hold an arbitary value.
> > |
> > | * We'll always treat X4 as the data register, since EX_DATA_REG_DATA is
> > | extracted from bits [4:0]. Thus we will corrupt X4 and cause arbitrary
> > | behaviour within load_unaligned_zeropad() and its caller.
> > |
> > | Fix this by extracting both values from ex->data as originally intended.
> >
> > > Fixes: 753b3236
> >
> > That should be expanded, e.g.
> >
> > Fixes: 753b32368705c396 ("arm64: extable: add load_unaligned_zeropad() handler")
> >
> > With those changes:
> >
> > Reviewed-by: Mark Rutland <[email protected]>
>
> Looking again, sicne this isn't jsut a null-deref, can we also rework the
> title, something like:
>
> | arm64: extable: fix load_unaligned_zeropad() reg indices
That's a much better commit message, thank you! I'll upload v2 shortly.
This was found by updating to a newer QEMU that correctly delivers MTE
faults from unaligned memory accesses, and triggers this bug reliably
during Android boot. I'll add a stack trace to v2.
>
> Thanks,
> Mark.
On Tue, Jan 25, 2022 at 08:59:07AM -0800, Evgenii Stepanov wrote:
> On Tue, Jan 25, 2022 at 7:50 AM Mark Rutland <[email protected]> wrote:
> >
> > On Tue, Jan 25, 2022 at 03:23:20PM +0000, Mark Rutland wrote:
> > > On Fri, Jan 21, 2022 at 06:34:47PM -0800, Evgenii Stepanov wrote:
> > > > ex_handler_load_unaligned_zeropad extracts the source and data register
> > > > numbers from the wrong field of the exception table.
> > >
> > > Ouch. Did you find this by inspection, or did this show up in testing?
> > >
> > > Sorry about this.
> > >
> > > I think we should be a little more explicit as to exactly what goes wrong. How
> > > about:
> > >
> > > | In ex_handler_load_unaligned_zeropad() we erroneously extract the data and
> > > | addr register indices from ex->type rather than ex->data. As ex->type will
> > > | contain EX_TYPE_LOAD_UNALIGNED_ZEROPAD (i.e. 4):
> > > |
> > > | * We'll always treat X0 as the address register, since EX_DATA_REG_ADDR is
> > > | extracted from bits [9:5]. Thus, we may attempt to dereference an arbitrary
> > > | address as X0 may hold an arbitary value.
> > > |
> > > | * We'll always treat X4 as the data register, since EX_DATA_REG_DATA is
> > > | extracted from bits [4:0]. Thus we will corrupt X4 and cause arbitrary
> > > | behaviour within load_unaligned_zeropad() and its caller.
> > > |
> > > | Fix this by extracting both values from ex->data as originally intended.
> > >
> > > > Fixes: 753b3236
> > >
> > > That should be expanded, e.g.
> > >
> > > Fixes: 753b32368705c396 ("arm64: extable: add load_unaligned_zeropad() handler")
> > >
> > > With those changes:
> > >
> > > Reviewed-by: Mark Rutland <[email protected]>
> >
> > Looking again, sicne this isn't jsut a null-deref, can we also rework the
> > title, something like:
> >
> > | arm64: extable: fix load_unaligned_zeropad() reg indices
>
> That's a much better commit message, thank you! I'll upload v2 shortly.
>
> This was found by updating to a newer QEMU that correctly delivers MTE
> faults from unaligned memory accesses, and triggers this bug reliably
> during Android boot. I'll add a stack trace to v2.
That'd be great, thanks!
Mark.