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From: Marc Zyngier <maz@kernel.org>
To: Steven Price <steven.price@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>,
	linux-kernel@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org,
	Andrey Konovalov <andreyknvl@google.com>,
	Alexander Potapenko <glider@google.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Vincenzo Frascino <vincenzo.frascino@arm.com>,
	Will Deacon <will@kernel.org>,
	kvmarm@lists.cs.columbia.edu
Subject: Re: [PATCH] KVM: arm64: Compute TPIDR_EL2 ignoring MTE tag
Date: Fri, 08 Jan 2021 16:51:11 +0000	[thread overview]
Message-ID: <e49459f08d0afb30a120dfb3d6b80741@kernel.org> (raw)
In-Reply-To: <20210108161254.53674-1-steven.price@arm.com>

Hi Steven,

On 2021-01-08 16:12, Steven Price wrote:
> KASAN in HW_TAGS mode will store MTE tags in the top byte of the
> pointer. When computing the offset for TPIDR_EL2 we don't want anything
> in the top byte, so remove the tag to ensure the computation is correct
> no matter what the tag.
> 
> Fixes: 94ab5b61ee16 ("kasan, arm64: enable CONFIG_KASAN_HW_TAGS")
> Signed-off-by: Steven Price <steven.price@arm.com>
> ---
> Without this fix I can't boot a config with KASAN_HW_TAGS and KVM on an
> MTE enabled host. I'm unsure if this should really be in
> this_cpu_ptr_nvhe_sym().

this_cpu_ptr_nvhe_sym() should return something that is valid for
the EL1 kernel, so I guess untagging in the helper may not be
that useful.

However, I'm more concerned by anything at requires us to follow
pointers set up by EL1 at EL2. It looks to me that the only reason
the whole thing works is because kern_hyp_va() *accidentally* drops
tags before applying the EL1/EL2 offset...

Or am I getting it wrong?

Thanks,

         M.
-- 
Jazz is not dead. It just smells funny...
_______________________________________________
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: Marc Zyngier <maz@kernel.org>
To: Steven Price <steven.price@arm.com>
Cc: Suzuki K Poulose <suzuki.poulose@arm.com>,
	Catalin Marinas <catalin.marinas@arm.com>,
	linux-kernel@vger.kernel.org, James Morse <james.morse@arm.com>,
	linux-arm-kernel@lists.infradead.org,
	Andrey Konovalov <andreyknvl@google.com>,
	Alexander Potapenko <glider@google.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Vincenzo Frascino <vincenzo.frascino@arm.com>,
	Will Deacon <will@kernel.org>,
	kvmarm@lists.cs.columbia.edu,
	Julien Thierry <julien.thierry.kdev@gmail.com>
Subject: Re: [PATCH] KVM: arm64: Compute TPIDR_EL2 ignoring MTE tag
Date: Fri, 08 Jan 2021 16:51:11 +0000	[thread overview]
Message-ID: <e49459f08d0afb30a120dfb3d6b80741@kernel.org> (raw)
In-Reply-To: <20210108161254.53674-1-steven.price@arm.com>

Hi Steven,

On 2021-01-08 16:12, Steven Price wrote:
> KASAN in HW_TAGS mode will store MTE tags in the top byte of the
> pointer. When computing the offset for TPIDR_EL2 we don't want anything
> in the top byte, so remove the tag to ensure the computation is correct
> no matter what the tag.
> 
> Fixes: 94ab5b61ee16 ("kasan, arm64: enable CONFIG_KASAN_HW_TAGS")
> Signed-off-by: Steven Price <steven.price@arm.com>
> ---
> Without this fix I can't boot a config with KASAN_HW_TAGS and KVM on an
> MTE enabled host. I'm unsure if this should really be in
> this_cpu_ptr_nvhe_sym().

this_cpu_ptr_nvhe_sym() should return something that is valid for
the EL1 kernel, so I guess untagging in the helper may not be
that useful.

However, I'm more concerned by anything at requires us to follow
pointers set up by EL1 at EL2. It looks to me that the only reason
the whole thing works is because kern_hyp_va() *accidentally* drops
tags before applying the EL1/EL2 offset...

Or am I getting it wrong?

Thanks,

         M.
-- 
Jazz is not dead. It just smells funny...

_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

WARNING: multiple messages have this Message-ID (diff)
From: Marc Zyngier <maz@kernel.org>
To: Steven Price <steven.price@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>,
	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,
	Alexander Potapenko <glider@google.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Andrey Konovalov <andreyknvl@google.com>,
	Vincenzo Frascino <vincenzo.frascino@arm.com>
Subject: Re: [PATCH] KVM: arm64: Compute TPIDR_EL2 ignoring MTE tag
Date: Fri, 08 Jan 2021 16:51:11 +0000	[thread overview]
Message-ID: <e49459f08d0afb30a120dfb3d6b80741@kernel.org> (raw)
In-Reply-To: <20210108161254.53674-1-steven.price@arm.com>

Hi Steven,

On 2021-01-08 16:12, Steven Price wrote:
> KASAN in HW_TAGS mode will store MTE tags in the top byte of the
> pointer. When computing the offset for TPIDR_EL2 we don't want anything
> in the top byte, so remove the tag to ensure the computation is correct
> no matter what the tag.
> 
> Fixes: 94ab5b61ee16 ("kasan, arm64: enable CONFIG_KASAN_HW_TAGS")
> Signed-off-by: Steven Price <steven.price@arm.com>
> ---
> Without this fix I can't boot a config with KASAN_HW_TAGS and KVM on an
> MTE enabled host. I'm unsure if this should really be in
> this_cpu_ptr_nvhe_sym().

this_cpu_ptr_nvhe_sym() should return something that is valid for
the EL1 kernel, so I guess untagging in the helper may not be
that useful.

However, I'm more concerned by anything at requires us to follow
pointers set up by EL1 at EL2. It looks to me that the only reason
the whole thing works is because kern_hyp_va() *accidentally* drops
tags before applying the EL1/EL2 offset...

Or am I getting it wrong?

Thanks,

         M.
-- 
Jazz is not dead. It just smells funny...

  reply	other threads:[~2021-01-08 16:51 UTC|newest]

Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-01-08 16:12 [PATCH] KVM: arm64: Compute TPIDR_EL2 ignoring MTE tag Steven Price
2021-01-08 16:12 ` Steven Price
2021-01-08 16:12 ` Steven Price
2021-01-08 16:51 ` Marc Zyngier [this message]
2021-01-08 16:51   ` Marc Zyngier
2021-01-08 16:51   ` Marc Zyngier
2021-01-08 17:03   ` Steven Price
2021-01-08 17:03     ` Steven Price
2021-01-08 17:03     ` Steven Price

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