[PATCH v3 13/20] arm64: entry: Hook up entry trampoline to exception vectors

Will Deacon
2017-12-06T12:38:47Z

Hook up the entry trampoline to our exception vectors so that all
exceptions from and returns to EL0 go via the trampoline, which swizzles
the vector base register accordingly. Transitioning to and from the
kernel clobbers x30, so we use tpidrro_el0 and far_el1 as scratch
registers for native tasks.

Reviewed-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
---
arch/arm64/kernel/entry.S | 39 ++++++++++++++++++++++++++++++++++++---
1 file changed, 36 insertions(+), 3 deletions(-)

diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
index b99fc928119c..39e3873b8d5a 100644
--- a/arch/arm64/kernel/entry.S
+++ b/arch/arm64/kernel/entry.S
@@ -73,6 +73,17 @@

.macro kernel_ventry, el, label, regsize = 64
.align 7
+#ifdef CONFIG_UNMAP_KERNEL_AT_EL0
+ .if \el == 0
+ .if \regsize == 64
+ mrs x30, tpidrro_el0
+ msr tpidrro_el0, xzr
+ .else
+ mov x30, xzr
+ .endif
+ .endif
+#endif
+
sub sp, sp, #S_FRAME_SIZE
#ifdef CONFIG_VMAP_STACK
/*
@@ -119,6 +130,11 @@
b el\()\el\()_\label
.endm

+ .macro tramp_alias, dst, sym
+ mov_q \dst, TRAMP_VALIAS
+ add \dst, \dst, #(\sym - .entry.tramp.text)
+ .endm
+
.macro kernel_entry, el, regsize = 64
.if \regsize == 32
mov w0, w0 // zero upper 32 bits of x0
@@ -271,18 +287,20 @@ alternative_else_nop_endif
.if \el == 0
ldr x23, [sp, #S_SP] // load return stack pointer
msr sp_el0, x23
+ tst x22, #PSR_MODE32_BIT // native task?
+ b.eq 3f
+
#ifdef CONFIG_ARM64_ERRATUM_845719
alternative_if ARM64_WORKAROUND_845719
- tbz x22, #4, 1f
#ifdef CONFIG_PID_IN_CONTEXTIDR
mrs x29, contextidr_el1
msr contextidr_el1, x29
#else
msr contextidr_el1, xzr
#endif
-1:
alternative_else_nop_endif
#endif
+3:
.endif

msr elr_el1, x21 // set up the return data
@@ -304,7 +322,22 @@ alternative_else_nop_endif
ldp x28, x29, [sp, #16 * 14]
ldr lr, [sp, #S_LR]
add sp, sp, #S_FRAME_SIZE // restore sp
- eret // return to kernel
+
+#ifndef CONFIG_UNMAP_KERNEL_AT_EL0
+ eret
+#else
+ .if \el == 0
+ bne 4f
+ msr far_el1, x30
+ tramp_alias x30, tramp_exit_native
+ br x30
+4:
+ tramp_alias x30, tramp_exit_compat
+ br x30
+ .else
+ eret
+ .endif
+#endif
.endm

.macro irq_stack_entry
--
2.1.4