Messages in this thread | | | Date | Tue, 25 Jan 2022 15:23:20 +0000 | From | Mark Rutland <> | Subject | Re: [PATCH] arm64: extable: fix null deref in load_unaligned_zeropad. |
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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 <mark.rutland@arm.com>
Thanks, Mark.
> Signed-off-by: Evgenii Stepanov <eugenis@google.com> > --- > 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 >
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