From: Catalin Marinas <catalin.marinas@arm.com>
To: Steven Price <steven.price@arm.com>
Cc: Marc Zyngier <maz@kernel.org>, Will Deacon <will@kernel.org>,
James Morse <james.morse@arm.com>,
Julien Thierry <julien.thierry.kdev@gmail.com>,
Suzuki K Poulose <suzuki.poulose@arm.com>,
kvmarm@lists.cs.columbia.edu,
linux-arm-kernel@lists.infradead.org,
linux-kernel@vger.kernel.org, Dave Martin <Dave.Martin@arm.com>,
Mark Rutland <mark.rutland@arm.com>,
Thomas Gleixner <tglx@linutronix.de>,
qemu-devel@nongnu.org, Juan Quintela <quintela@redhat.com>,
"Dr. David Alan Gilbert" <dgilbert@redhat.com>,
Richard Henderson <richard.henderson@linaro.org>,
Peter Maydell <peter.maydell@linaro.org>,
Haibo Xu <Haibo.Xu@arm.com>, Andrew Jones <drjones@redhat.com>
Subject: Re: [PATCH v11 1/6] arm64: mte: Sync tags for pages where PTE is untagged
Date: Tue, 4 May 2021 16:29:40 +0100 [thread overview]
Message-ID: <20210504152938.GC8078@arm.com> (raw)
In-Reply-To: <0ab0017c-1eaf-201e-587f-101e03da6b80@arm.com>
On Thu, Apr 29, 2021 at 05:06:05PM +0100, Steven Price wrote:
> On 27/04/2021 18:43, Catalin Marinas wrote:
> > On Fri, Apr 16, 2021 at 04:43:04PM +0100, Steven Price wrote:
> > > diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
> > > index e17b96d0e4b5..cf4b52a33b3c 100644
> > > --- a/arch/arm64/include/asm/pgtable.h
> > > +++ b/arch/arm64/include/asm/pgtable.h
> > > @@ -312,7 +312,7 @@ static inline void set_pte_at(struct mm_struct *mm, unsigned long addr,
> > > __sync_icache_dcache(pte);
> > > if (system_supports_mte() &&
> > > - pte_present(pte) && pte_tagged(pte) && !pte_special(pte))
> > > + pte_present(pte) && (pte_val(pte) & PTE_USER) && !pte_special(pte))
> >
> > I would add a pte_user() macro here or, if we restore the tags only when
> > the page is readable, use pte_access_permitted(pte, false). Also add a
> > comment why we do this.
>
> pte_access_permitted() looks like it describes what we want (user space can
> access the memory). I'll add the following comment:
>
> /*
> * If the PTE would provide user space will access to the tags
I think drop "will".
> * associated with it then ensure that the MTE tags are synchronised.
> * Exec-only mappings don't expose tags (instruction fetches don't
> * check tags).
> */
Sounds fine.
> > There's also the pte_user_exec() case which may not have the PTE_USER
> > set (exec-only permission) but I don't think it matters. We don't do tag
> > checking on instruction fetches, so if the user adds a PROT_READ to it,
> > it would go through set_pte_at() again. I'm not sure KVM does anything
> > special with exec-only mappings at stage 2, I suspect they won't be
> > accessible by the guest (but needs checking).
>
> It comes down to the behaviour of get_user_pages(). AFAICT that will fail if
> the memory is exec-only, so no stage 2 mapping will be created. Which of
> course means the guest can't do anything with that memory. That certainly
> seems like the only sane behaviour even without MTE.
That's my understanding as well. The get_user_pages_fast() path uses
pte_access_permitted() and should return false. The slower
get_user_pages() relies on checking the vma flags and it checks for
VM_READ.
--
Catalin
WARNING: multiple messages have this Message-ID (diff)
From: Catalin Marinas <catalin.marinas@arm.com>
To: Steven Price <steven.price@arm.com>
Cc: Mark Rutland <mark.rutland@arm.com>,
Peter Maydell <peter.maydell@linaro.org>,
"Dr. David Alan Gilbert" <dgilbert@redhat.com>,
Andrew Jones <drjones@redhat.com>, Haibo Xu <Haibo.Xu@arm.com>,
Suzuki K Poulose <suzuki.poulose@arm.com>,
qemu-devel@nongnu.org, Marc Zyngier <maz@kernel.org>,
Juan Quintela <quintela@redhat.com>,
Richard Henderson <richard.henderson@linaro.org>,
linux-kernel@vger.kernel.org, Dave Martin <Dave.Martin@arm.com>,
James Morse <james.morse@arm.com>,
linux-arm-kernel@lists.infradead.org,
Thomas Gleixner <tglx@linutronix.de>,
Will Deacon <will@kernel.org>,
kvmarm@lists.cs.columbia.edu,
Julien Thierry <julien.thierry.kdev@gmail.com>
Subject: Re: [PATCH v11 1/6] arm64: mte: Sync tags for pages where PTE is untagged
Date: Tue, 4 May 2021 16:29:40 +0100 [thread overview]
Message-ID: <20210504152938.GC8078@arm.com> (raw)
In-Reply-To: <0ab0017c-1eaf-201e-587f-101e03da6b80@arm.com>
On Thu, Apr 29, 2021 at 05:06:05PM +0100, Steven Price wrote:
> On 27/04/2021 18:43, Catalin Marinas wrote:
> > On Fri, Apr 16, 2021 at 04:43:04PM +0100, Steven Price wrote:
> > > diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
> > > index e17b96d0e4b5..cf4b52a33b3c 100644
> > > --- a/arch/arm64/include/asm/pgtable.h
> > > +++ b/arch/arm64/include/asm/pgtable.h
> > > @@ -312,7 +312,7 @@ static inline void set_pte_at(struct mm_struct *mm, unsigned long addr,
> > > __sync_icache_dcache(pte);
> > > if (system_supports_mte() &&
> > > - pte_present(pte) && pte_tagged(pte) && !pte_special(pte))
> > > + pte_present(pte) && (pte_val(pte) & PTE_USER) && !pte_special(pte))
> >
> > I would add a pte_user() macro here or, if we restore the tags only when
> > the page is readable, use pte_access_permitted(pte, false). Also add a
> > comment why we do this.
>
> pte_access_permitted() looks like it describes what we want (user space can
> access the memory). I'll add the following comment:
>
> /*
> * If the PTE would provide user space will access to the tags
I think drop "will".
> * associated with it then ensure that the MTE tags are synchronised.
> * Exec-only mappings don't expose tags (instruction fetches don't
> * check tags).
> */
Sounds fine.
> > There's also the pte_user_exec() case which may not have the PTE_USER
> > set (exec-only permission) but I don't think it matters. We don't do tag
> > checking on instruction fetches, so if the user adds a PROT_READ to it,
> > it would go through set_pte_at() again. I'm not sure KVM does anything
> > special with exec-only mappings at stage 2, I suspect they won't be
> > accessible by the guest (but needs checking).
>
> It comes down to the behaviour of get_user_pages(). AFAICT that will fail if
> the memory is exec-only, so no stage 2 mapping will be created. Which of
> course means the guest can't do anything with that memory. That certainly
> seems like the only sane behaviour even without MTE.
That's my understanding as well. The get_user_pages_fast() path uses
pte_access_permitted() and should return false. The slower
get_user_pages() relies on checking the vma flags and it checks for
VM_READ.
--
Catalin
WARNING: multiple messages have this Message-ID (diff)
From: Catalin Marinas <catalin.marinas@arm.com>
To: Steven Price <steven.price@arm.com>
Cc: "Dr. David Alan Gilbert" <dgilbert@redhat.com>,
qemu-devel@nongnu.org, Marc Zyngier <maz@kernel.org>,
Juan Quintela <quintela@redhat.com>,
Richard Henderson <richard.henderson@linaro.org>,
linux-kernel@vger.kernel.org, Dave Martin <Dave.Martin@arm.com>,
linux-arm-kernel@lists.infradead.org,
Thomas Gleixner <tglx@linutronix.de>,
Will Deacon <will@kernel.org>,
kvmarm@lists.cs.columbia.edu
Subject: Re: [PATCH v11 1/6] arm64: mte: Sync tags for pages where PTE is untagged
Date: Tue, 4 May 2021 16:29:40 +0100 [thread overview]
Message-ID: <20210504152938.GC8078@arm.com> (raw)
In-Reply-To: <0ab0017c-1eaf-201e-587f-101e03da6b80@arm.com>
On Thu, Apr 29, 2021 at 05:06:05PM +0100, Steven Price wrote:
> On 27/04/2021 18:43, Catalin Marinas wrote:
> > On Fri, Apr 16, 2021 at 04:43:04PM +0100, Steven Price wrote:
> > > diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
> > > index e17b96d0e4b5..cf4b52a33b3c 100644
> > > --- a/arch/arm64/include/asm/pgtable.h
> > > +++ b/arch/arm64/include/asm/pgtable.h
> > > @@ -312,7 +312,7 @@ static inline void set_pte_at(struct mm_struct *mm, unsigned long addr,
> > > __sync_icache_dcache(pte);
> > > if (system_supports_mte() &&
> > > - pte_present(pte) && pte_tagged(pte) && !pte_special(pte))
> > > + pte_present(pte) && (pte_val(pte) & PTE_USER) && !pte_special(pte))
> >
> > I would add a pte_user() macro here or, if we restore the tags only when
> > the page is readable, use pte_access_permitted(pte, false). Also add a
> > comment why we do this.
>
> pte_access_permitted() looks like it describes what we want (user space can
> access the memory). I'll add the following comment:
>
> /*
> * If the PTE would provide user space will access to the tags
I think drop "will".
> * associated with it then ensure that the MTE tags are synchronised.
> * Exec-only mappings don't expose tags (instruction fetches don't
> * check tags).
> */
Sounds fine.
> > There's also the pte_user_exec() case which may not have the PTE_USER
> > set (exec-only permission) but I don't think it matters. We don't do tag
> > checking on instruction fetches, so if the user adds a PROT_READ to it,
> > it would go through set_pte_at() again. I'm not sure KVM does anything
> > special with exec-only mappings at stage 2, I suspect they won't be
> > accessible by the guest (but needs checking).
>
> It comes down to the behaviour of get_user_pages(). AFAICT that will fail if
> the memory is exec-only, so no stage 2 mapping will be created. Which of
> course means the guest can't do anything with that memory. That certainly
> seems like the only sane behaviour even without MTE.
That's my understanding as well. The get_user_pages_fast() path uses
pte_access_permitted() and should return false. The slower
get_user_pages() relies on checking the vma flags and it checks for
VM_READ.
--
Catalin
_______________________________________________
kvmarm mailing list
kvmarm@lists.cs.columbia.edu
https://lists.cs.columbia.edu/mailman/listinfo/kvmarm
WARNING: multiple messages have this Message-ID (diff)
From: Catalin Marinas <catalin.marinas@arm.com>
To: Steven Price <steven.price@arm.com>
Cc: Marc Zyngier <maz@kernel.org>, Will Deacon <will@kernel.org>,
James Morse <james.morse@arm.com>,
Julien Thierry <julien.thierry.kdev@gmail.com>,
Suzuki K Poulose <suzuki.poulose@arm.com>,
kvmarm@lists.cs.columbia.edu,
linux-arm-kernel@lists.infradead.org,
linux-kernel@vger.kernel.org, Dave Martin <Dave.Martin@arm.com>,
Mark Rutland <mark.rutland@arm.com>,
Thomas Gleixner <tglx@linutronix.de>,
qemu-devel@nongnu.org, Juan Quintela <quintela@redhat.com>,
"Dr. David Alan Gilbert" <dgilbert@redhat.com>,
Richard Henderson <richard.henderson@linaro.org>,
Peter Maydell <peter.maydell@linaro.org>,
Haibo Xu <Haibo.Xu@arm.com>, Andrew Jones <drjones@redhat.com>
Subject: Re: [PATCH v11 1/6] arm64: mte: Sync tags for pages where PTE is untagged
Date: Tue, 4 May 2021 16:29:40 +0100 [thread overview]
Message-ID: <20210504152938.GC8078@arm.com> (raw)
In-Reply-To: <0ab0017c-1eaf-201e-587f-101e03da6b80@arm.com>
On Thu, Apr 29, 2021 at 05:06:05PM +0100, Steven Price wrote:
> On 27/04/2021 18:43, Catalin Marinas wrote:
> > On Fri, Apr 16, 2021 at 04:43:04PM +0100, Steven Price wrote:
> > > diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
> > > index e17b96d0e4b5..cf4b52a33b3c 100644
> > > --- a/arch/arm64/include/asm/pgtable.h
> > > +++ b/arch/arm64/include/asm/pgtable.h
> > > @@ -312,7 +312,7 @@ static inline void set_pte_at(struct mm_struct *mm, unsigned long addr,
> > > __sync_icache_dcache(pte);
> > > if (system_supports_mte() &&
> > > - pte_present(pte) && pte_tagged(pte) && !pte_special(pte))
> > > + pte_present(pte) && (pte_val(pte) & PTE_USER) && !pte_special(pte))
> >
> > I would add a pte_user() macro here or, if we restore the tags only when
> > the page is readable, use pte_access_permitted(pte, false). Also add a
> > comment why we do this.
>
> pte_access_permitted() looks like it describes what we want (user space can
> access the memory). I'll add the following comment:
>
> /*
> * If the PTE would provide user space will access to the tags
I think drop "will".
> * associated with it then ensure that the MTE tags are synchronised.
> * Exec-only mappings don't expose tags (instruction fetches don't
> * check tags).
> */
Sounds fine.
> > There's also the pte_user_exec() case which may not have the PTE_USER
> > set (exec-only permission) but I don't think it matters. We don't do tag
> > checking on instruction fetches, so if the user adds a PROT_READ to it,
> > it would go through set_pte_at() again. I'm not sure KVM does anything
> > special with exec-only mappings at stage 2, I suspect they won't be
> > accessible by the guest (but needs checking).
>
> It comes down to the behaviour of get_user_pages(). AFAICT that will fail if
> the memory is exec-only, so no stage 2 mapping will be created. Which of
> course means the guest can't do anything with that memory. That certainly
> seems like the only sane behaviour even without MTE.
That's my understanding as well. The get_user_pages_fast() path uses
pte_access_permitted() and should return false. The slower
get_user_pages() relies on checking the vma flags and it checks for
VM_READ.
--
Catalin
_______________________________________________
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:[~2021-05-04 15:29 UTC|newest]
Thread overview: 104+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-16 15:43 [PATCH v11 0/6] MTE support for KVM guest Steven Price
2021-04-16 15:43 ` Steven Price
2021-04-16 15:43 ` Steven Price
2021-04-16 15:43 ` Steven Price
2021-04-16 15:43 ` [PATCH v11 1/6] arm64: mte: Sync tags for pages where PTE is untagged Steven Price
2021-04-16 15:43 ` Steven Price
2021-04-16 15:43 ` Steven Price
2021-04-16 15:43 ` Steven Price
2021-04-27 17:43 ` Catalin Marinas
2021-04-27 17:43 ` Catalin Marinas
2021-04-27 17:43 ` Catalin Marinas
2021-04-27 17:43 ` Catalin Marinas
2021-04-29 16:06 ` Steven Price
2021-04-29 16:06 ` Steven Price
2021-04-29 16:06 ` Steven Price
2021-04-29 16:06 ` Steven Price
2021-05-04 15:29 ` Catalin Marinas [this message]
2021-05-04 15:29 ` Catalin Marinas
2021-05-04 15:29 ` Catalin Marinas
2021-05-04 15:29 ` Catalin Marinas
2021-04-16 15:43 ` [PATCH v11 2/6] arm64: kvm: Introduce MTE VM feature Steven Price
2021-04-16 15:43 ` Steven Price
2021-04-16 15:43 ` Steven Price
2021-04-16 15:43 ` Steven Price
2021-04-28 17:07 ` Catalin Marinas
2021-04-28 17:07 ` Catalin Marinas
2021-04-28 17:07 ` Catalin Marinas
2021-04-28 17:07 ` Catalin Marinas
2021-04-29 16:06 ` Steven Price
2021-04-29 16:06 ` Steven Price
2021-04-29 16:06 ` Steven Price
2021-04-29 16:06 ` Steven Price
2021-05-04 17:40 ` Catalin Marinas
2021-05-04 17:40 ` Catalin Marinas
2021-05-04 17:40 ` Catalin Marinas
2021-05-04 17:40 ` Catalin Marinas
2021-05-06 16:15 ` Steven Price
2021-05-06 16:15 ` Steven Price
2021-05-06 16:15 ` Steven Price
2021-05-06 16:15 ` Steven Price
2021-05-07 18:25 ` Catalin Marinas
2021-05-07 18:25 ` Catalin Marinas
2021-05-07 18:25 ` Catalin Marinas
2021-05-07 18:25 ` Catalin Marinas
2021-05-10 18:35 ` Catalin Marinas
2021-05-10 18:35 ` Catalin Marinas
2021-05-10 18:35 ` Catalin Marinas
2021-05-10 18:35 ` Catalin Marinas
2021-05-12 15:46 ` Steven Price
2021-05-12 15:46 ` Steven Price
2021-05-12 15:46 ` Steven Price
2021-05-12 15:46 ` Steven Price
2021-05-12 17:45 ` Catalin Marinas
2021-05-12 17:45 ` Catalin Marinas
2021-05-12 17:45 ` Catalin Marinas
2021-05-12 17:45 ` Catalin Marinas
2021-05-13 10:57 ` Steven Price
2021-05-13 10:57 ` Steven Price
2021-05-13 10:57 ` Steven Price
2021-05-13 10:57 ` Steven Price
2021-05-13 15:08 ` Catalin Marinas
2021-05-13 15:08 ` Catalin Marinas
2021-05-13 15:08 ` Catalin Marinas
2021-05-13 15:08 ` Catalin Marinas
2021-05-13 15:21 ` Catalin Marinas
2021-05-13 15:21 ` Catalin Marinas
2021-05-13 15:21 ` Catalin Marinas
2021-05-13 15:21 ` Catalin Marinas
2021-04-16 15:43 ` [PATCH v11 3/6] arm64: kvm: Save/restore MTE registers Steven Price
2021-04-16 15:43 ` Steven Price
2021-04-16 15:43 ` Steven Price
2021-04-16 15:43 ` Steven Price
2021-04-16 15:43 ` [PATCH v11 4/6] arm64: kvm: Expose KVM_ARM_CAP_MTE Steven Price
2021-04-16 15:43 ` Steven Price
2021-04-16 15:43 ` Steven Price
2021-04-16 15:43 ` Steven Price
2021-04-16 15:43 ` [PATCH v11 5/6] KVM: arm64: ioctl to fetch/store tags in a guest Steven Price
2021-04-16 15:43 ` Steven Price
2021-04-16 15:43 ` Steven Price
2021-04-16 15:43 ` Steven Price
2021-04-27 17:58 ` Catalin Marinas
2021-04-27 17:58 ` Catalin Marinas
2021-04-27 17:58 ` Catalin Marinas
2021-04-27 17:58 ` Catalin Marinas
2021-04-29 16:06 ` Steven Price
2021-04-29 16:06 ` Steven Price
2021-04-29 16:06 ` Steven Price
2021-04-29 16:06 ` Steven Price
2021-05-04 17:44 ` Catalin Marinas
2021-05-04 17:44 ` Catalin Marinas
2021-05-04 17:44 ` Catalin Marinas
2021-05-04 17:44 ` Catalin Marinas
2021-05-07 9:44 ` Steven Price
2021-05-07 9:44 ` Steven Price
2021-05-07 9:44 ` Steven Price
2021-05-07 9:44 ` Steven Price
2021-05-07 9:59 ` David Laight
2021-05-07 9:59 ` David Laight
2021-05-07 9:59 ` David Laight
2021-05-07 9:59 ` David Laight
2021-04-16 15:43 ` [PATCH v11 6/6] KVM: arm64: Document MTE capability and ioctl Steven Price
2021-04-16 15:43 ` Steven Price
2021-04-16 15:43 ` Steven Price
2021-04-16 15:43 ` Steven Price
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