Date: Mon, 15 Jan 2018 12:24:59 +0000
From: Dave P Martin <Dave.Martin@arm.com>
To: Kees Cook <keescook@chromium.org>
Cc: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Catalin Marinas <Catalin.Marinas@arm.com>,
        Will Deacon <Will.Deacon@arm.com>,
        Christian Borntraeger <borntraeger@de.ibm.com>,
        Ingo Molnar <mingo@kernel.org>,
        James Morse <James.Morse@arm.com>,
        "Peter Zijlstra (Intel)" <peterz@infradead.org>,
        zijun_hu <zijun_hu@htc.com>,
        "linux-arm-kernel@lists.infradead.org" 
        <linux-arm-kernel@lists.infradead.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        David Windsor <dave@nullcore.net>,
        Alexander Viro <viro@zeniv.linux.org.uk>,
        Andrew Morton <akpm@linux-foundation.org>,
        Andy Lutomirski <luto@kernel.org>,
        Christoph Hellwig <hch@infradead.org>,
        Christoph Lameter <cl@linux.com>,
        "David S. Miller" <davem@davemloft.net>,
        Laura Abbott <labbott@redhat.com>,
        Mark Rutland <Mark.Rutland@arm.com>,
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        Paolo Bonzini <pbonzini@redhat.com>,
        Christoffer Dall <christoffer.dall@linaro.org>,
        Dave Kleikamp <dave.kleikamp@oracle.com>,
        Jan Kara <jack@suse.cz>,
        Luis de Bethencourt <luisbg@kernel.org>,
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        Matthew Garrett <mjg59@google.com>,
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        <kernel-hardening@lists.openwall.com>
Subject: Re: [PATCH 33/38] arm64: Implement thread_struct whitelist for
 hardened usercopy
Message-ID: <20180115122458.GI12608@e103592.cambridge.arm.com>
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On Thu, Jan 11, 2018 at 02:03:05AM +0000, Kees Cook wrote:
> This whitelists the FPU register state portion of the thread_struct for
> copying to userspace, instead of the default entire structure.
>
> Cc: Catalin Marinas <catalin.marinas@arm.com>
> Cc: Will Deacon <will.deacon@arm.com>
> Cc: Christian Borntraeger <borntraeger@de.ibm.com>
> Cc: Ingo Molnar <mingo@kernel.org>
> Cc: James Morse <james.morse@arm.com>
> Cc: "Peter Zijlstra (Intel)" <peterz@infradead.org>
> Cc: Dave Martin <Dave.Martin@arm.com>
> Cc: zijun_hu <zijun_hu@htc.com>
> Cc: linux-arm-kernel@lists.infradead.org
> Signed-off-by: Kees Cook <keescook@chromium.org>
> ---
>  arch/arm64/Kconfig                 | 1 +
>  arch/arm64/include/asm/processor.h | 8 ++++++++
>  2 files changed, 9 insertions(+)
>
> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> index a93339f5178f..c84477e6a884 100644
> --- a/arch/arm64/Kconfig
> +++ b/arch/arm64/Kconfig
> @@ -90,6 +90,7 @@ config ARM64
>       select HAVE_ARCH_MMAP_RND_BITS
>       select HAVE_ARCH_MMAP_RND_COMPAT_BITS if COMPAT
>       select HAVE_ARCH_SECCOMP_FILTER
> +     select HAVE_ARCH_THREAD_STRUCT_WHITELIST
>       select HAVE_ARCH_TRACEHOOK
>       select HAVE_ARCH_TRANSPARENT_HUGEPAGE
>       select HAVE_ARCH_VMAP_STACK
> diff --git a/arch/arm64/include/asm/processor.h b/arch/arm64/include/asm/processor.h
> index 023cacb946c3..e58a5864ec89 100644
> --- a/arch/arm64/include/asm/processor.h
> +++ b/arch/arm64/include/asm/processor.h
> @@ -113,6 +113,14 @@ struct thread_struct {
>       struct debug_info       debug;          /* debugging */
>  };
>
> +/* Whitelist the fpsimd_state for copying to userspace. */
> +static inline void arch_thread_struct_whitelist(unsigned long *offset,
> +                                             unsigned long *size)
> +{
> +     *offset = offsetof(struct thread_struct, fpsimd_state);
> +     *size = sizeof(struct fpsimd_state);

This should be fpsimd_state.user_fpsimd (fpsimd_state.cpu is important
for correctly context switching and not supposed to be user-accessible.
A user copy that encompasses that is definitely a bug).

Cheers
---Dave
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