* [PATCH] arm64: mte: Allow PTRACE_PEEKMTETAGS access to the zero page
@ 2021-02-10 18:03 Catalin Marinas
2021-02-10 18:52 ` Luis Machado
` (2 more replies)
0 siblings, 3 replies; 6+ messages in thread
From: Catalin Marinas @ 2021-02-10 18:03 UTC (permalink / raw)
To: linux-arm-kernel
Cc: Luis Machado, Kevin Brodsky, Vincenzo Frascino, Steven Price,
stable, Will Deacon
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));
/* limit access to the end of the page */
offset = offset_in_page(addr);
^ permalink raw reply related [flat|nested] 6+ messages in thread
* Re: [PATCH] arm64: mte: Allow PTRACE_PEEKMTETAGS access to the zero page
2021-02-10 18:03 [PATCH] arm64: mte: Allow PTRACE_PEEKMTETAGS access to the zero page Catalin Marinas
@ 2021-02-10 18:52 ` Luis Machado
2021-02-11 10:35 ` Catalin Marinas
2021-02-11 10:56 ` Vincenzo Frascino
2021-02-12 16:45 ` Catalin Marinas
2 siblings, 1 reply; 6+ messages in thread
From: Luis Machado @ 2021-02-10 18:52 UTC (permalink / raw)
To: Catalin Marinas, linux-arm-kernel
Cc: Kevin Brodsky, Vincenzo Frascino, Steven Price, stable,
Will Deacon, David Spickett
On 2/10/21 3:03 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));
>
> /* limit access to the end of the page */
> offset = offset_in_page(addr);
>
Thanks. I gave this a try and it works as expected. So memory that is
PROT_MTE but has not been accessed yet can be inspected with PEEKMTETAGS
without getting an EIO back.
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH] arm64: mte: Allow PTRACE_PEEKMTETAGS access to the zero page
2021-02-10 18:52 ` Luis Machado
@ 2021-02-11 10:35 ` Catalin Marinas
0 siblings, 0 replies; 6+ messages in thread
From: Catalin Marinas @ 2021-02-11 10:35 UTC (permalink / raw)
To: Luis Machado
Cc: linux-arm-kernel, Kevin Brodsky, Vincenzo Frascino, Steven Price,
stable, Will Deacon, David Spickett
On Wed, Feb 10, 2021 at 03:52:18PM -0300, Luis Machado wrote:
> On 2/10/21 3:03 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>
[...]
> Thanks. I gave this a try and it works as expected. So memory that is
> PROT_MTE but has not been accessed yet can be inspected with PEEKMTETAGS
> without getting an EIO back.
Thanks. I assume I can add your tested-by.
--
Catalin
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH] arm64: mte: Allow PTRACE_PEEKMTETAGS access to the zero page
2021-02-10 18:03 [PATCH] arm64: mte: Allow PTRACE_PEEKMTETAGS access to the zero page Catalin Marinas
2021-02-10 18:52 ` Luis Machado
@ 2021-02-11 10:56 ` Vincenzo Frascino
2021-02-12 16:45 ` Catalin Marinas
2 siblings, 0 replies; 6+ messages in thread
From: Vincenzo Frascino @ 2021-02-11 10:56 UTC (permalink / raw)
To: Catalin Marinas, linux-arm-kernel
Cc: Luis Machado, Kevin Brodsky, Steven Price, stable, Will Deacon
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
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH] arm64: mte: Allow PTRACE_PEEKMTETAGS access to the zero page
2021-02-10 18:03 [PATCH] arm64: mte: Allow PTRACE_PEEKMTETAGS access to the zero page Catalin Marinas
2021-02-10 18:52 ` Luis Machado
2021-02-11 10:56 ` Vincenzo Frascino
@ 2021-02-12 16:45 ` Catalin Marinas
2 siblings, 0 replies; 6+ messages in thread
From: Catalin Marinas @ 2021-02-12 16:45 UTC (permalink / raw)
To: linux-arm-kernel, Catalin Marinas
Cc: Will Deacon, Kevin Brodsky, Steven Price, stable,
Vincenzo Frascino, Luis Machado
On Wed, 10 Feb 2021 18:03:16 +0000, 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.
>
> [...]
Applied to arm64 (for-next/fixes), thanks!
[1/1] arm64: mte: Allow PTRACE_PEEKMTETAGS access to the zero page
https://git.kernel.org/arm64/c/68d54ceeec0e
--
Catalin
^ permalink raw reply [flat|nested] 6+ messages in thread
* [PATCH] arm64: mte: Allow PTRACE_PEEKMTETAGS access to the zero page
@ 2021-02-16 18:56 vivek
0 siblings, 0 replies; 6+ messages in thread
From: vivek @ 2021-02-16 18:56 UTC (permalink / raw)
To: bitu.kv; +Cc: Catalin Marinas, # 5 . 10 . x, Will Deacon
From: Catalin Marinas <catalin.marinas@arm.com>
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
---
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 e99edde..3e6331b 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 dc9ada6..80b62fe 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));
/* limit access to the end of the page */
offset = offset_in_page(addr);
--
2.7.4
^ permalink raw reply related [flat|nested] 6+ messages in thread
end of thread, other threads:[~2021-02-16 18:57 UTC | newest]
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2021-02-10 18:03 [PATCH] arm64: mte: Allow PTRACE_PEEKMTETAGS access to the zero page Catalin Marinas
2021-02-10 18:52 ` Luis Machado
2021-02-11 10:35 ` Catalin Marinas
2021-02-11 10:56 ` Vincenzo Frascino
2021-02-12 16:45 ` Catalin Marinas
2021-02-16 18:56 vivek
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