| Message ID | 20230420214327.2357985-1-pcc@google.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | arm64: mte: Do not set PG_mte_tagged if tags were not initialized | expand |
On Thu, Apr 20, 2023 at 02:43:27PM -0700, Peter Collingbourne wrote: > The mte_sync_page_tags() function sets PG_mte_tagged if it initializes > page tags. Then we return to mte_sync_tags(), which sets PG_mte_tagged > again. At best, this is redundant. However, it is possible for > mte_sync_page_tags() to return without having initialized tags for the > page, i.e. in the case where check_swap is true (non-compound page), > is_swap_pte(old_pte) is false and pte_is_tagged is false. So at worst, > we set PG_mte_tagged on a page with uninitialized tags. This can happen > if, for example, page migration causes a PTE for an untagged page to > be replaced. If the userspace program subsequently uses mprotect() to > enable PROT_MTE for that page, the uninitialized tags will be exposed > to userspace. > > Fix it by removing the redundant call to set_page_mte_tagged(). > > Fixes: e059853d14ca ("arm64: mte: Fix/clarify the PG_mte_tagged semantics") > Signed-off-by: Peter Collingbourne <pcc@google.com> > Cc: <stable@vger.kernel.org> # 6.1 > Link: https://linux-review.googlesource.com/id/Ib02d004d435b2ed87603b858ef7480f7b1463052 > --- > arch/arm64/kernel/mte.c | 7 ++----- > 1 file changed, 2 insertions(+), 5 deletions(-) > > diff --git a/arch/arm64/kernel/mte.c b/arch/arm64/kernel/mte.c > index f5bcb0dc6267..7e89968bd282 100644 > --- a/arch/arm64/kernel/mte.c > +++ b/arch/arm64/kernel/mte.c > @@ -66,13 +66,10 @@ void mte_sync_tags(pte_t old_pte, pte_t pte) > return; > > /* if PG_mte_tagged is set, tags have already been initialised */ > - for (i = 0; i < nr_pages; i++, page++) { > - if (!page_mte_tagged(page)) { > + for (i = 0; i < nr_pages; i++, page++) > + if (!page_mte_tagged(page)) > mte_sync_page_tags(page, old_pte, check_swap, > pte_is_tagged); > - set_page_mte_tagged(page); > - } > - } It makes sense, not sure why I added it here when mte_sync_page_tags() was already setting the flag if needed. Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
On Thu, 20 Apr 2023 14:43:27 -0700, Peter Collingbourne wrote: > The mte_sync_page_tags() function sets PG_mte_tagged if it initializes > page tags. Then we return to mte_sync_tags(), which sets PG_mte_tagged > again. At best, this is redundant. However, it is possible for > mte_sync_page_tags() to return without having initialized tags for the > page, i.e. in the case where check_swap is true (non-compound page), > is_swap_pte(old_pte) is false and pte_is_tagged is false. So at worst, > we set PG_mte_tagged on a page with uninitialized tags. This can happen > if, for example, page migration causes a PTE for an untagged page to > be replaced. If the userspace program subsequently uses mprotect() to > enable PROT_MTE for that page, the uninitialized tags will be exposed > to userspace. > > [...] Applied to arm64 (for-next/fixes), thanks! [1/1] arm64: mte: Do not set PG_mte_tagged if tags were not initialized https://git.kernel.org/arm64/c/c4c597f1b367 Cheers,
diff --git a/arch/arm64/kernel/mte.c b/arch/arm64/kernel/mte.c index f5bcb0dc6267..7e89968bd282 100644 --- a/arch/arm64/kernel/mte.c +++ b/arch/arm64/kernel/mte.c @@ -66,13 +66,10 @@ void mte_sync_tags(pte_t old_pte, pte_t pte) return; /* if PG_mte_tagged is set, tags have already been initialised */ - for (i = 0; i < nr_pages; i++, page++) { - if (!page_mte_tagged(page)) { + for (i = 0; i < nr_pages; i++, page++) + if (!page_mte_tagged(page)) mte_sync_page_tags(page, old_pte, check_swap, pte_is_tagged); - set_page_mte_tagged(page); - } - } /* ensure the tags are visible before the PTE is set */ smp_wmb();
The mte_sync_page_tags() function sets PG_mte_tagged if it initializes page tags. Then we return to mte_sync_tags(), which sets PG_mte_tagged again. At best, this is redundant. However, it is possible for mte_sync_page_tags() to return without having initialized tags for the page, i.e. in the case where check_swap is true (non-compound page), is_swap_pte(old_pte) is false and pte_is_tagged is false. So at worst, we set PG_mte_tagged on a page with uninitialized tags. This can happen if, for example, page migration causes a PTE for an untagged page to be replaced. If the userspace program subsequently uses mprotect() to enable PROT_MTE for that page, the uninitialized tags will be exposed to userspace. Fix it by removing the redundant call to set_page_mte_tagged(). Fixes: e059853d14ca ("arm64: mte: Fix/clarify the PG_mte_tagged semantics") Signed-off-by: Peter Collingbourne <pcc@google.com> Cc: <stable@vger.kernel.org> # 6.1 Link: https://linux-review.googlesource.com/id/Ib02d004d435b2ed87603b858ef7480f7b1463052 --- arch/arm64/kernel/mte.c | 7 ++----- 1 file changed, 2 insertions(+), 5 deletions(-)