diff options
| author | Catalin Marinas <catalin.marinas@arm.com> | 2021-02-10 18:03:16 +0000 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2021-02-17 11:02:28 +0100 |
| commit | 975a2396e37cecc42ba006d69d943be149efbeb0 (patch) | |
| tree | 6383af52b2bc582051d8ee1f5860e481f5aa31d7 | |
| parent | 3ed6cc9c2dd08a2ed29f43b5916cb16c3318e98a (diff) | |
arm64: mte: Allow PTRACE_PEEKMTETAGS access to the zero page
commit 68d54ceeec0e5fee4fb8048e6a04c193f32525ca upstream.
The ptrace(PTRACE_PEEKMTETAGS) implementation checks whether the user
page has valid tags (mapped with PROT_MTE) by testing the PG_mte_tagged
page flag. If this bit is cleared, ptrace(PTRACE_PEEKMTETAGS) returns
-EIO.
A newly created (PROT_MTE) mapping points to the zero page which had its
tags zeroed during cpu_enable_mte(). If there were no prior writes to
this mapping, ptrace(PTRACE_PEEKMTETAGS) fails with -EIO since the zero
page does not have the PG_mte_tagged flag set.
Set PG_mte_tagged on the zero page when its tags are cleared during
boot. In addition, to avoid ptrace(PTRACE_PEEKMTETAGS) succeeding on
!PROT_MTE mappings pointing to the zero page, change the
__access_remote_tags() check to (vm_flags & VM_MTE) instead of
PG_mte_tagged.
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Fixes: 34bfeea4a9e9 ("arm64: mte: Clear the tags when a page is mapped in user-space with PROT_MTE")
Cc: <stable@vger.kernel.org> # 5.10.x
Cc: Will Deacon <will@kernel.org>
Reported-by: Luis Machado <luis.machado@linaro.org>
Tested-by: Luis Machado <luis.machado@linaro.org>
Reviewed-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
Link: https://lore.kernel.org/r/20210210180316.23654-1-catalin.marinas@arm.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
| -rw-r--r-- | arch/arm64/kernel/cpufeature.c | 6 | ||||
| -rw-r--r-- | arch/arm64/kernel/mte.c | 3 |
2 files changed, 3 insertions, 6 deletions
diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c index 0a52e076153b..65a522fbd874 100644 --- a/arch/arm64/kernel/cpufeature.c +++ b/arch/arm64/kernel/cpufeature.c @@ -1696,16 +1696,12 @@ static void bti_enable(const struct arm64_cpu_capabilities *__unused) #ifdef CONFIG_ARM64_MTE static void cpu_enable_mte(struct arm64_cpu_capabilities const *cap) { - static bool cleared_zero_page = false; - /* * Clear the tags in the zero page. This needs to be done via the * linear map which has the Tagged attribute. */ - if (!cleared_zero_page) { - cleared_zero_page = true; + if (!test_and_set_bit(PG_mte_tagged, &ZERO_PAGE(0)->flags)) mte_clear_page_tags(lm_alias(empty_zero_page)); - } } #endif /* CONFIG_ARM64_MTE */ diff --git a/arch/arm64/kernel/mte.c b/arch/arm64/kernel/mte.c index ef15c8a2a49d..7a66a7d9c1ff 100644 --- a/arch/arm64/kernel/mte.c +++ b/arch/arm64/kernel/mte.c @@ -239,11 +239,12 @@ static int __access_remote_tags(struct mm_struct *mm, unsigned long addr, * would cause the existing tags to be cleared if the page * was never mapped with PROT_MTE. */ - if (!test_bit(PG_mte_tagged, &page->flags)) { + if (!(vma->vm_flags & VM_MTE)) { ret = -EOPNOTSUPP; put_page(page); break; } + WARN_ON_ONCE(!test_bit(PG_mte_tagged, &page->flags)); /* limit access to the end of the page */ offset = offset_in_page(addr); |