From 49003a8d6b35e128ef5e51433e60e783a46fbe5f Mon Sep 17 00:00:00 2001 From: James Morse Date: Thu, 10 Dec 2015 10:22:41 +0000 Subject: [PATCH] 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: James Morse Signed-off-by: Will Deacon --- arch/arm64/kernel/entry.S | 2 ++ 1 file changed, 2 insertions(+) diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S index e394f8c9595a..2284c296e3f7 100644 --- a/arch/arm64/kernel/entry.S +++ b/arch/arm64/kernel/entry.S @@ -93,6 +93,8 @@ and tsk, tsk, #~(THREAD_SIZE - 1) // Ensure MDSCR_EL1.SS is clear, ldr x19, [tsk, #TI_FLAGS] // since we can unmask debug disable_step_tsk x19, x20 // exceptions when scheduling. + + mov x29, xzr // fp pointed to user-space .else add x21, sp, #S_FRAME_SIZE .endif -- 2.34.1