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Commit 66e48a0d authored by Dave Martin's avatar Dave Martin Committed by Marc Zyngier
Browse files

arm64: fpsimd: Avoid FPSIMD context leakage for the init task 



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: default avatarDave Martin <Dave.Martin@arm.com>
Fixes: 005f78cd ("arm64: defer reloading a task's FPSIMD state to userland resume")
Reviewed-by: default avatarCatalin Marinas <catalin.marinas@arm.com>
Reviewed-by: default avatarAlex Bennée <alex.bennee@linaro.org>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: default avatarMarc Zyngier <marc.zyngier@arm.com>
parent d1797615

arch/arm64/include/asm/thread_info.h

+7 −6
Original line number Diff line number Diff line
@@ -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 */