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Commit 49003a8d authored by James Morse's avatar James Morse Committed by Will Deacon
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arm64: don't call C code with el0's fp register 



On entry from el0, we save all the registers on the kernel stack, and
restore them before returning. x29 remains unchanged when we call out
to C code, which will store x29 as the frame-pointer on the stack.

Instead, write 0 into x29 after entry from el0, to avoid any risk of
tracing into user space.

Signed-off-by: default avatarJames Morse <james.morse@arm.com>
Signed-off-by: default avatarWill Deacon <will.deacon@arm.com>
parent 1ffe199b

arch/arm64/kernel/entry.S

+2 −0
Original line number Original line Diff line number Diff line
@@ -93,6 +93,8 @@ 
	and	tsk, tsk, #~(THREAD_SIZE - 1)	// Ensure MDSCR_EL1.SS is clear,

	and	tsk, tsk, #~(THREAD_SIZE - 1)	// Ensure MDSCR_EL1.SS is clear,

	ldr	x19, [tsk, #TI_FLAGS]		// since we can unmask debug

	ldr	x19, [tsk, #TI_FLAGS]		// since we can unmask debug

	disable_step_tsk x19, x20		// exceptions when scheduling.

	disable_step_tsk x19, x20		// exceptions when scheduling.



	mov	x29, xzr			// fp pointed to user-space

	.else

	.else

	add	x21, sp, #S_FRAME_SIZE

	add	x21, sp, #S_FRAME_SIZE

	.endif

	.endif