Dave Martin <Dave.Martin@xxxxxxx> 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@xxxxxxx>
> Fixes: 005f78cd8849 ("arm64: defer reloading a task's FPSIMD state to userland resume")
> Reviewed-by: Catalin Marinas <catalin.marinas@xxxxxxx>
> Reviewed-by: Alex Bennée <alex.bennee@xxxxxxxxxx>
Still good ;-)
> Cc: Will Deacon <will.deacon@xxxxxxx>
> Cc: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx>
>
> ---
>
> 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
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