Commit 8e99cb45 authored by Vincenzo Frascino's avatar Vincenzo Frascino Committed by Stephen Rothwell
Browse files

arm64: mte: reset the page tag in page->flags

The hardware tag-based KASAN for compatibility with the other modes stores
the tag associated to a page in page->flags.  Due to this the kernel
faults on access when it allocates a page with an initial tag and the user
changes the tags.

Reset the tag associated by the kernel to a page in all the meaningful
places to prevent kernel faults on access.

Note: An alternative to this approach could be to modify page_to_virt().
This though could end up being racy, in fact if a CPU checks the
PG_mte_tagged bit and decides that the page is not tagged but another CPU
maps the same with PROT_MTE and becomes tagged the subsequent kernel
access would fail.

Link: https://lkml.kernel.org/r/9073d4e973747a6f78d5bdd7ebe17f290d087096.1606161801.git.andreyknvl@google.com

Signed-off-by: Vincenzo Frascino's avatarVincenzo Frascino <vincenzo.frascino@arm.com>
Signed-off-by: default avatarAndrey Konovalov <andreyknvl@google.com>
Reviewed-by: Catalin Marinas's avatarCatalin Marinas <catalin.marinas@arm.com>
Tested-by: Vincenzo Frascino's avatarVincenzo Frascino <vincenzo.frascino@arm.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Branislav Rankov <Branislav.Rankov@arm.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Evgenii Stepanov <eugenis@google.com>
Cc: Kevin Brodsky <kevin.brodsky@arm.com>
Cc: Marco Elver <elver@google.com>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Cc: Will Deacon <will.deacon@arm.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarStephen Rothwell <sfr@canb.auug.org.au>
parent 5dad87cd
......@@ -371,6 +371,11 @@ static void swsusp_mte_restore_tags(void)
unsigned long pfn = xa_state.xa_index;
struct page *page = pfn_to_online_page(pfn);
/*
* It is not required to invoke page_kasan_tag_reset(page)
* at this point since the tags stored in page->flags are
* already restored.
*/
mte_restore_page_tags(page_address(page), tags);
mte_free_tag_storage(tags);
......
......@@ -34,6 +34,15 @@ static void mte_sync_page_tags(struct page *page, pte_t *ptep, bool check_swap)
return;
}
page_kasan_tag_reset(page);
/*
* We need smp_wmb() in between setting the flags and clearing the
* tags because if another thread reads page->flags and builds a
* tagged address out of it, there is an actual dependency to the
* memory access, but on the current thread we do not guarantee that
* the new page->flags are visible before the tags were updated.
*/
smp_wmb();
mte_clear_page_tags(page_address(page));
}
......
......@@ -23,6 +23,15 @@ void copy_highpage(struct page *to, struct page *from)
if (system_supports_mte() && test_bit(PG_mte_tagged, &from->flags)) {
set_bit(PG_mte_tagged, &to->flags);
page_kasan_tag_reset(to);
/*
* We need smp_wmb() in between setting the flags and clearing the
* tags because if another thread reads page->flags and builds a
* tagged address out of it, there is an actual dependency to the
* memory access, but on the current thread we do not guarantee that
* the new page->flags are visible before the tags were updated.
*/
smp_wmb();
mte_copy_page_tags(kto, kfrom);
}
}
......
......@@ -53,6 +53,15 @@ bool mte_restore_tags(swp_entry_t entry, struct page *page)
if (!tags)
return false;
page_kasan_tag_reset(page);
/*
* We need smp_wmb() in between setting the flags and clearing the
* tags because if another thread reads page->flags and builds a
* tagged address out of it, there is an actual dependency to the
* memory access, but on the current thread we do not guarantee that
* the new page->flags are visible before the tags were updated.
*/
smp_wmb();
mte_restore_page_tags(page_address(page), tags);
return true;
......
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