[kernel-hardening] Re: [PATCH 33/38] arm64: Implement thread_struct whitelist for hardened usercopy

Dave P Martin
2018-01-15T12:24:59Z

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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