Re: [PATCH v11 07/19] arm64: fpsimd: Avoid FPSIMD context leakage for the init task

["Alex Bennée" <alex.bennee@linaro.org>]

Dave Martin <Dave.Martin@arm.com> writes:

> The init task is started with thread_flags equal to 0, which means
> that TIF_FOREIGN_FPSTATE is initially clear.
>
> It is theoretically possible (if unlikely) that the init task could
> reach userspace without ever being scheduled out.  If this occurs,
> data left in the FPSIMD registers by the kernel could be exposed.
>
> This patch fixes this anomaly by ensuring that the init task's
> initial TIF_FOREIGN_FPSTATE is set.
>
> Signed-off-by: Dave Martin <Dave.Martin@arm.com>
> Fixes: 005f78cd8849 ("arm64: defer reloading a task's FPSIMD state to userland resume")
> Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
> Reviewed-by: Alex Bennée <alex.bennee@linaro.org>

Still good ;-)

> Cc: Will Deacon <will.deacon@arm.com>
> Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
>
> ---
>
> Changes since v10:
>
>  * New patch.
> ---
>  arch/arm64/include/asm/thread_info.h | 13 +++++++------
>  1 file changed, 7 insertions(+), 6 deletions(-)
>
> diff --git a/arch/arm64/include/asm/thread_info.h b/arch/arm64/include/asm/thread_info.h
> index 740aa03c..af271f9 100644
> --- a/arch/arm64/include/asm/thread_info.h
> +++ b/arch/arm64/include/asm/thread_info.h
> @@ -45,12 +45,6 @@ struct thread_info {
>  	int			preempt_count;	/* 0 => preemptable, <0 => bug */
>  };
>
> -#define INIT_THREAD_INFO(tsk)						\
> -{									\
> -	.preempt_count	= INIT_PREEMPT_COUNT,				\
> -	.addr_limit	= KERNEL_DS,					\
> -}
> -
>  #define thread_saved_pc(tsk)	\
>  	((unsigned long)(tsk->thread.cpu_context.pc))
>  #define thread_saved_sp(tsk)	\
> @@ -117,5 +111,12 @@ void arch_release_task_struct(struct task_struct *tsk);
>  				 _TIF_SYSCALL_TRACEPOINT | _TIF_SECCOMP | \
>  				 _TIF_NOHZ)
>
> +#define INIT_THREAD_INFO(tsk)						\
> +{									\
> +	.flags		= _TIF_FOREIGN_FPSTATE,				\
> +	.preempt_count	= INIT_PREEMPT_COUNT,				\
> +	.addr_limit	= KERNEL_DS,					\
> +}
> +
>  #endif /* __KERNEL__ */
>  #endif /* __ASM_THREAD_INFO_H */


--
Alex Bennée
_______________________________________________
kvmarm mailing list
kvmarm@lists.cs.columbia.edu
https://lists.cs.columbia.edu/mailman/listinfo/kvmarm