arm64: don't call C code with el0's fp register
authorJames Morse <james.morse@arm.com>
Thu, 10 Dec 2015 10:22:41 +0000 (10:22 +0000)
committerWill Deacon <will.deacon@arm.com>
Thu, 10 Dec 2015 12:08:09 +0000 (12:08 +0000)
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 <james.morse@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
arch/arm64/kernel/entry.S

index e394f8c9595a493f00c083f1d0733ad1fdca5a27..2284c296e3f71a11286d0969e067285977bc42f6 100644 (file)
@@ -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