From: Vincenzo Frascino <vincenzo.frascino@arm.com> To: Catalin Marinas <catalin.marinas@arm.com>, linux-arm-kernel@lists.infradead.org Cc: Luis Machado <luis.machado@linaro.org>, Kevin Brodsky <kevin.brodsky@arm.com>, Steven Price <steven.price@arm.com>, stable@vger.kernel.org, Will Deacon <will@kernel.org> Subject: Re: [PATCH] arm64: mte: Allow PTRACE_PEEKMTETAGS access to the zero page Date: Thu, 11 Feb 2021 10:56:46 +0000 [thread overview] Message-ID: <aa94d2b9-d2f1-04fd-7cfe-8a1ab078e5c3@arm.com> (raw) In-Reply-To: <20210210180316.23654-1-catalin.marinas@arm.com> On 2/10/21 6:03 PM, Catalin Marinas wrote: > 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> > --- > > The fix is actually checking VM_MTE instead of PG_mte_tagged in > __access_remote_tags() but I added the WARN_ON(!PG_mte_tagged) and > setting the flag on the zero page in case we break this assumption in > the future. > > arch/arm64/kernel/cpufeature.c | 6 +----- > 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 e99eddec0a46..3e6331b64932 100644 > --- a/arch/arm64/kernel/cpufeature.c > +++ b/arch/arm64/kernel/cpufeature.c > @@ -1701,16 +1701,12 @@ 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)); > - } > > kasan_init_hw_tags_cpu(); > } > diff --git a/arch/arm64/kernel/mte.c b/arch/arm64/kernel/mte.c > index dc9ada64feed..80b62fe49dcf 100644 > --- a/arch/arm64/kernel/mte.c > +++ b/arch/arm64/kernel/mte.c > @@ -329,11 +329,12 @@ 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)); > Nit: I would live a white line before WARN_ON_ONCE() to improve readability and maybe transform it in WARN_ONCE() with a message (alternatively a comment on top) based on what you are explaining in the commit message. Otherwise: Reviewed-by: Vincenzo Frascino <vincenzo.frascino@arm.com> > /* limit access to the end of the page */ > offset = offset_in_page(addr); > -- Regards, Vincenzo
WARNING: multiple messages have this Message-ID (diff)
From: Vincenzo Frascino <vincenzo.frascino@arm.com> To: Catalin Marinas <catalin.marinas@arm.com>, linux-arm-kernel@lists.infradead.org Cc: Will Deacon <will@kernel.org>, Kevin Brodsky <kevin.brodsky@arm.com>, Luis Machado <luis.machado@linaro.org>, stable@vger.kernel.org, Steven Price <steven.price@arm.com> Subject: Re: [PATCH] arm64: mte: Allow PTRACE_PEEKMTETAGS access to the zero page Date: Thu, 11 Feb 2021 10:56:46 +0000 [thread overview] Message-ID: <aa94d2b9-d2f1-04fd-7cfe-8a1ab078e5c3@arm.com> (raw) In-Reply-To: <20210210180316.23654-1-catalin.marinas@arm.com> On 2/10/21 6:03 PM, Catalin Marinas wrote: > 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> > --- > > The fix is actually checking VM_MTE instead of PG_mte_tagged in > __access_remote_tags() but I added the WARN_ON(!PG_mte_tagged) and > setting the flag on the zero page in case we break this assumption in > the future. > > arch/arm64/kernel/cpufeature.c | 6 +----- > 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 e99eddec0a46..3e6331b64932 100644 > --- a/arch/arm64/kernel/cpufeature.c > +++ b/arch/arm64/kernel/cpufeature.c > @@ -1701,16 +1701,12 @@ 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)); > - } > > kasan_init_hw_tags_cpu(); > } > diff --git a/arch/arm64/kernel/mte.c b/arch/arm64/kernel/mte.c > index dc9ada64feed..80b62fe49dcf 100644 > --- a/arch/arm64/kernel/mte.c > +++ b/arch/arm64/kernel/mte.c > @@ -329,11 +329,12 @@ 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)); > Nit: I would live a white line before WARN_ON_ONCE() to improve readability and maybe transform it in WARN_ONCE() with a message (alternatively a comment on top) based on what you are explaining in the commit message. Otherwise: Reviewed-by: Vincenzo Frascino <vincenzo.frascino@arm.com> > /* limit access to the end of the page */ > offset = offset_in_page(addr); > -- Regards, Vincenzo _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
next prev parent reply other threads:[~2021-02-11 10:57 UTC|newest] Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top 2021-02-10 18:03 [PATCH] arm64: mte: Allow PTRACE_PEEKMTETAGS access to the zero page Catalin Marinas 2021-02-10 18:03 ` Catalin Marinas 2021-02-10 18:52 ` Luis Machado 2021-02-10 18:52 ` Luis Machado 2021-02-11 10:35 ` Catalin Marinas 2021-02-11 10:35 ` Catalin Marinas 2021-02-11 10:56 ` Vincenzo Frascino [this message] 2021-02-11 10:56 ` Vincenzo Frascino 2021-02-12 16:45 ` Catalin Marinas 2021-02-12 16:45 ` Catalin Marinas 2021-02-16 18:56 vivek
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