set to zero the x0-x17 registers
As per the SMCCC v1.2 spec, unused result and scratch registers can leak information after an SMC call. We can mitigate against this risk by returning zero in each register.
The leakage we are referring to is data leakage across exception levels. The intent is to prevent lower exception levels (EL1/EL0) from reading the SMC data exchanged at EL2.
Signed-off-by: Abdellatif El Khlifi abdellatif.elkhlifi@arm.com Cc: Tom Rini trini@konsulko.com Cc: Simon Glass sjg@chromium.org Cc: Ilias Apalodimas ilias.apalodimas@linaro.org Cc: Jens Wiklander jens.wiklander@linaro.org ---
Changelog: ===============
v4:
* move the clearing code into a new macro: clear_gp_regs
v3:
* clear the Xn registers after SMC calls
arch/arm/cpu/armv8/smccc-call.S | 9 +++++++++ 1 file changed, 9 insertions(+)
diff --git a/arch/arm/cpu/armv8/smccc-call.S b/arch/arm/cpu/armv8/smccc-call.S index ec6f299bc9..32f3eb8eeb 100644 --- a/arch/arm/cpu/armv8/smccc-call.S +++ b/arch/arm/cpu/armv8/smccc-call.S @@ -50,6 +50,12 @@ ENDPROC(__arm_smccc_hvc)
#ifdef CONFIG_ARM64
+ .macro clear_gp_regs + .irp n,0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17 + mov x\n, xzr + .endr + .endm + .macro SMCCC_1_2 instr /* Save `res` and free a GPR that won't be clobbered */ stp x1, x19, [sp, #-16]! @@ -84,6 +90,9 @@ ENDPROC(__arm_smccc_hvc) stp x14, x15, [x19, #ARM_SMCCC_1_2_REGS_X14_OFFS] stp x16, x17, [x19, #ARM_SMCCC_1_2_REGS_X16_OFFS]
+ /* x0-x17 registers can leak information after an SMC or HVC call. Let's clear them */ + clear_gp_regs + /* Restore original x19 */ ldp xzr, x19, [sp], #16 ret