| Patrick Williams | 8dd6848 | 2022-10-04 07:57:18 -0500 | [diff] [blame] | 1 | From 83f9da30247c2d021658bc1b595c59ecc35eadf5 Mon Sep 17 00:00:00 2001 |
| 2 | From: Abdellatif El Khlifi <abdellatif.elkhlifi@arm.com> |
| 3 | Date: Fri, 29 Jul 2022 13:07:43 +0100 |
| 4 | Subject: [PATCH 07/26] arm64: smccc: clear the Xn registers after SMC calls |
| 5 | |
| 6 | set to zero the x0-x17 registers |
| 7 | |
| 8 | As per the SMCCC v1.2 spec, unused result and scratch registers can leak |
| 9 | information after an SMC call. We can mitigate against this risk by |
| 10 | returning zero in each register. |
| 11 | |
| 12 | Signed-off-by: Abdellatif El Khlifi <abdellatif.elkhlifi@arm.com> |
| 13 | Upstream-Status: Submitted [cover letter: https://lore.kernel.org/all/20220926101723.9965-1-abdellatif.elkhlifi@arm.com/] |
| 14 | --- |
| 15 | |
| 16 | Changelog: |
| 17 | =============== |
| 18 | |
| 19 | v4: |
| 20 | |
| 21 | * move the clearing code into a new macro: clear_gp_regs |
| 22 | |
| 23 | v3: |
| 24 | |
| 25 | * clear the Xn registers after SMC calls |
| 26 | |
| 27 | arch/arm/cpu/armv8/smccc-call.S | 9 +++++++++ |
| 28 | 1 file changed, 9 insertions(+) |
| 29 | |
| 30 | diff --git a/arch/arm/cpu/armv8/smccc-call.S b/arch/arm/cpu/armv8/smccc-call.S |
| 31 | index ec6f299bc9..32f3eb8eeb 100644 |
| 32 | --- a/arch/arm/cpu/armv8/smccc-call.S |
| 33 | +++ b/arch/arm/cpu/armv8/smccc-call.S |
| 34 | @@ -50,6 +50,12 @@ ENDPROC(__arm_smccc_hvc) |
| 35 | |
| 36 | #ifdef CONFIG_ARM64 |
| 37 | |
| 38 | + .macro clear_gp_regs |
| 39 | + .irp n,0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17 |
| 40 | + mov x\n, xzr |
| 41 | + .endr |
| 42 | + .endm |
| 43 | + |
| 44 | .macro SMCCC_1_2 instr |
| 45 | /* Save `res` and free a GPR that won't be clobbered */ |
| 46 | stp x1, x19, [sp, #-16]! |
| 47 | @@ -84,6 +90,9 @@ ENDPROC(__arm_smccc_hvc) |
| 48 | stp x14, x15, [x19, #ARM_SMCCC_1_2_REGS_X14_OFFS] |
| 49 | stp x16, x17, [x19, #ARM_SMCCC_1_2_REGS_X16_OFFS] |
| 50 | |
| 51 | + /* x0-x17 registers can leak information after an SMC or HVC call. Let's clear them */ |
| 52 | + clear_gp_regs |
| 53 | + |
| 54 | /* Restore original x19 */ |
| 55 | ldp xzr, x19, [sp], #16 |
| 56 | ret |
| 57 | -- |
| 58 | 2.17.1 |
| 59 | |