From mboxrd@z Thu Jan 1 00:00:00 1970 From: laurent.pinchart@ideasonboard.com (Laurent Pinchart) Date: Sun, 13 Dec 2015 23:41:01 +0200 Subject: [PATCH 1/5] iommu/io-pgtable-arm: Avoid dereferencing bogus PTEs In-Reply-To: References: Message-ID: <7110327.9BOBJr0LiQ@avalon> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org Hi Robin, Thank you for the patch. On Friday 04 December 2015 17:52:58 Robin Murphy wrote: > In the case of corrupted page tables, or when an invalid size is given, > __arm_lpae_unmap() may recurse beyond the maximum number of levels. > Unfortunately the detection of this error condition only happens *after* > calculating a nonsense offset from something which might not be a valid > table pointer and dereferencing that to see if it is a valid PTE. > > Make things a little more robust by checking the level is valid before > doing anything which depends on it being so. > > Signed-off-by: Robin Murphy This looks good to me. Reviewed-by: Laurent Pinchart I'm curious though, have you seen this error in practice ? > --- > drivers/iommu/io-pgtable-arm.c | 8 +++++--- > 1 file changed, 5 insertions(+), 3 deletions(-) > > diff --git a/drivers/iommu/io-pgtable-arm.c b/drivers/iommu/io-pgtable-arm.c > index 7df9777..366a354 100644 > --- a/drivers/iommu/io-pgtable-arm.c > +++ b/drivers/iommu/io-pgtable-arm.c > @@ -486,11 +486,13 @@ static int __arm_lpae_unmap(struct arm_lpae_io_pgtable > *data, void *cookie = data->iop.cookie; > size_t blk_size = ARM_LPAE_BLOCK_SIZE(lvl, data); > > + /* Something went horribly wrong and we ran out of page table */ > + if (WARN_ON(lvl == ARM_LPAE_MAX_LEVELS)) > + return 0; > + > ptep += ARM_LPAE_LVL_IDX(iova, lvl, data); > pte = *ptep; > - > - /* Something went horribly wrong and we ran out of page table */ > - if (WARN_ON(!pte || (lvl == ARM_LPAE_MAX_LEVELS))) > + if (WARN_ON(!pte)) > return 0; > > /* If the size matches this level, we're in the right place */ -- Regards, Laurent Pinchart