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SubjectRe: [PATCH 14/14] arm64: Add ARM_SMCCC_ARCH_WORKAROUND_1 BP hardening support
On 29 January 2018 at 10:07, Marc Zyngier <marc.zyngier@arm.com> wrote:
> On 29/01/18 09:42, Ard Biesheuvel wrote:
>> On 29 January 2018 at 09:36, Marc Zyngier <marc.zyngier@arm.com> wrote:
>>> On 28/01/18 23:08, Ard Biesheuvel wrote:
>>>> On 26 January 2018 at 14:28, Marc Zyngier <marc.zyngier@arm.com> wrote:
>>>>> Add the detection and runtime code for ARM_SMCCC_ARCH_WORKAROUND_1.
>>>>> It is lovely. Really.
>>>>>
>>>>> Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
>>>>> ---
>>>>> arch/arm64/kernel/bpi.S | 20 ++++++++++++
>>>>> arch/arm64/kernel/cpu_errata.c | 71 +++++++++++++++++++++++++++++++++++++++++-
>>>>> 2 files changed, 90 insertions(+), 1 deletion(-)
>>>>>
>>>>> diff --git a/arch/arm64/kernel/bpi.S b/arch/arm64/kernel/bpi.S
>>>>> index 76225c2611ea..add7e08a018d 100644
>>>>> --- a/arch/arm64/kernel/bpi.S
>>>>> +++ b/arch/arm64/kernel/bpi.S
>>>>> @@ -17,6 +17,7 @@
>>>>> */
>>>>>
>>>>> #include <linux/linkage.h>
>>>>> +#include <linux/arm-smccc.h>
>>>>>
>>>>> .macro ventry target
>>>>> .rept 31
>>>>> @@ -85,3 +86,22 @@ ENTRY(__qcom_hyp_sanitize_link_stack_start)
>>>>> .endr
>>>>> ldp x29, x30, [sp], #16
>>>>> ENTRY(__qcom_hyp_sanitize_link_stack_end)
>>>>> +
>>>>> +.macro smccc_workaround_1 inst
>>>>> + sub sp, sp, #(8 * 4)
>>>>> + stp x2, x3, [sp, #(16 * 0)]
>>>>> + stp x0, x1, [sp, #(16 * 1)]
>>>>> + orr w0, wzr, #ARM_SMCCC_ARCH_WORKAROUND_1
>>>>> + \inst #0
>>>>> + ldp x2, x3, [sp, #(16 * 0)]
>>>>> + ldp x0, x1, [sp, #(16 * 1)]
>>>>> + add sp, sp, #(8 * 4)
>>>>> +.endm
>>>>> +
>>>>> +ENTRY(__smccc_workaround_1_smc_start)
>>>>> + smccc_workaround_1 smc
>>>>> +ENTRY(__smccc_workaround_1_smc_end)
>>>>> +
>>>>> +ENTRY(__smccc_workaround_1_hvc_start)
>>>>> + smccc_workaround_1 hvc
>>>>> +ENTRY(__smccc_workaround_1_hvc_end)
>>>>> diff --git a/arch/arm64/kernel/cpu_errata.c b/arch/arm64/kernel/cpu_errata.c
>>>>> index ed6881882231..f1501873f2e4 100644
>>>>> --- a/arch/arm64/kernel/cpu_errata.c
>>>>> +++ b/arch/arm64/kernel/cpu_errata.c
>>>>> @@ -70,6 +70,10 @@ DEFINE_PER_CPU_READ_MOSTLY(struct bp_hardening_data, bp_hardening_data);
>>>>> extern char __psci_hyp_bp_inval_start[], __psci_hyp_bp_inval_end[];
>>>>> extern char __qcom_hyp_sanitize_link_stack_start[];
>>>>> extern char __qcom_hyp_sanitize_link_stack_end[];
>>>>> +extern char __smccc_workaround_1_smc_start[];
>>>>> +extern char __smccc_workaround_1_smc_end[];
>>>>> +extern char __smccc_workaround_1_hvc_start[];
>>>>> +extern char __smccc_workaround_1_hvc_end[];
>>>>>
>>>>> static void __copy_hyp_vect_bpi(int slot, const char *hyp_vecs_start,
>>>>> const char *hyp_vecs_end)
>>>>> @@ -116,6 +120,10 @@ static void __install_bp_hardening_cb(bp_hardening_cb_t fn,
>>>>> #define __psci_hyp_bp_inval_end NULL
>>>>> #define __qcom_hyp_sanitize_link_stack_start NULL
>>>>> #define __qcom_hyp_sanitize_link_stack_end NULL
>>>>> +#define __smccc_workaround_1_smc_start NULL
>>>>> +#define __smccc_workaround_1_smc_end NULL
>>>>> +#define __smccc_workaround_1_hvc_start NULL
>>>>> +#define __smccc_workaround_1_hvc_end NULL
>>>>>
>>>>> static void __install_bp_hardening_cb(bp_hardening_cb_t fn,
>>>>> const char *hyp_vecs_start,
>>>>> @@ -142,17 +150,78 @@ static void install_bp_hardening_cb(const struct arm64_cpu_capabilities *entry,
>>>>> __install_bp_hardening_cb(fn, hyp_vecs_start, hyp_vecs_end);
>>>>> }
>>>>>
>>>>> +#include <uapi/linux/psci.h>
>>>>> +#include <linux/arm-smccc.h>
>>>>> #include <linux/psci.h>
>>>>>
>>>>> +static void call_smc_arch_workaround_1(void)
>>>>> +{
>>>>> + register int w0 asm("w0") = ARM_SMCCC_ARCH_WORKAROUND_1;
>>>>> + asm volatile("smc #0\n"
>>>>> + : "+r" (w0));
>>>>> +}
>>>>> +
>>>>> +static void call_hvc_arch_workaround_1(void)
>>>>> +{
>>>>> + register int w0 asm("w0") = ARM_SMCCC_ARCH_WORKAROUND_1;
>>>>> + asm volatile("hvc #0\n"
>>>>> + : "+r" (w0));
>>>>> +}
>>>>> +
>>>>> +static bool check_smccc_arch_workaround_1(const struct arm64_cpu_capabilities *entry)
>>>>> +{
>>>>> + bp_hardening_cb_t cb;
>>>>> + void *smccc_start, *smccc_end;
>>>>> + struct arm_smccc_res res;
>>>>> +
>>>>> + if (psci_ops.variant == SMCCC_VARIANT_1_0)
>>>>> + return false;
>>>>> +
>>>>> + switch (psci_ops.conduit) {
>>>>> + case PSCI_CONDUIT_HVC:
>>>>> + arm_smccc_hvc(ARM_SMCCC_ARCH_FEATURES_FUNC_ID,
>>>>> + ARM_SMCCC_ARCH_WORKAROUND_1, 0, 0, 0, 0, 0, 0,
>>>>> + &res);
>>>>> + if (res.a0)
>>>>> + return false;
>>>>> + cb = call_hvc_arch_workaround_1;
>>>>> + smccc_start = __smccc_workaround_1_hvc_start;
>>>>> + smccc_end = __smccc_workaround_1_hvc_end;
>>>>> + break;
>>>>> +
>>>>> + case PSCI_CONDUIT_SMC:
>>>>> + arm_smccc_smc(ARM_SMCCC_ARCH_FEATURES_FUNC_ID,
>>>>> + ARM_SMCCC_ARCH_WORKAROUND_1, 0, 0, 0, 0, 0, 0,
>>>>> + &res);
>>>>
>>>> This compiles to
>>>>
>>>> 4a8: 928fffe1 mov x1, #0xffffffffffff8000 // #-32768
>>>> 4ac: b26187e0 mov x0, #0xffffffff80000001 // #-2147483647
>>>> 4b0: d2800007 mov x7, #0x0 // #0
>>>> 4b4: d2800006 mov x6, #0x0 // #0
>>>> 4b8: d2800005 mov x5, #0x0 // #0
>>>> 4bc: d2800004 mov x4, #0x0 // #0
>>>> 4c0: d2800003 mov x3, #0x0 // #0
>>>> 4c4: d2800002 mov x2, #0x0 // #0
>>>> 4c8: f2b00001 movk x1, #0x8000, lsl #16
>>>> 4cc: 94000000 bl 0 <__arm_smccc_smc>
>>>>
>>>> so it seems we're missing a UL suffix somewhere.
>>>
>>> Yeah, this seems to stem from ARM_SMCCC_FAST_CALL, which is bit 31 and
>>> isn't advertised as unsigned. It still works because both x0 and x1 are
>>> used as 32bit quantities in this particular SMC context, but that has
>>> the potential of triggering unexpected behaviours in broken implementations.
>>>
>>
>> Are you sure about that? To me, it looks like this code
>>
>> static int32_t smccc_arch_features(u_register_t arg)
>> {
>> switch (arg) {
>> case SMCCC_VERSION:
>> case SMCCC_ARCH_FEATURES:
>> return SMC_OK;
>> #if WORKAROUND_CVE_2017_5715
>> case SMCCC_ARCH_WORKAROUND_1:
>> return SMC_OK;
>> #endif
>> default:
>> return SMC_UNK;
>> }
>> }
>>
>> will end up comparing 0xffffffff80008000 to 0x80008000, and fail
>> (which is what it did when I tried it)
>
> Good point. Only a0 is guaranteed to be evaluated as a 32bit register,
> and parameters can be used either way. Funny how long this stayed
> unnoticed. How about the patch below?
>
> M.
>
> From bbb79f54808b94c187cb1cbe56fecc0e2241576a Mon Sep 17 00:00:00 2001
> From: Marc Zyngier <marc.zyngier@arm.com>
> Date: Mon, 29 Jan 2018 09:48:28 +0000
> Subject: [PATCH] arm/arm64: smccc: Make function identifiers an unsigned
> quantity
>
> Function identifiers are a 32bit, unsigned quantify. But we never

quantiTy ^^^

> tell so to the compiler, resulting in the following:
>
> 4ac: b26187e0 mov x0, #0xffffffff80000001
>
> We thus rely on the firmware narrowing it for us, which is not
> always a reasonable expectation.
>
> Cc: stable@vger.kernel.org
> Reported-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
> Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
> ---
> include/linux/arm-smccc.h | 6 ++++--
> 1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/include/linux/arm-smccc.h b/include/linux/arm-smccc.h
> index ab1e86111953..e2af4ff772a1 100644
> --- a/include/linux/arm-smccc.h
> +++ b/include/linux/arm-smccc.h
> @@ -14,14 +14,16 @@
> #ifndef __LINUX_ARM_SMCCC_H
> #define __LINUX_ARM_SMCCC_H
>
> +#include <uapi/linux/const.h>
> +
> /*
> * This file provides common defines for ARM SMC Calling Convention as
> * specified in
> * http://infocenter.arm.com/help/topic/com.arm.doc.den0028a/index.html
> */
>
> -#define ARM_SMCCC_STD_CALL 0
> -#define ARM_SMCCC_FAST_CALL 1
> +#define ARM_SMCCC_STD_CALL _AC(0,U)
> +#define ARM_SMCCC_FAST_CALL _AC(1,U)
> #define ARM_SMCCC_TYPE_SHIFT 31
>
> #define ARM_SMCCC_SMC_32 0
> --
> 2.14.2
>

Acked-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Tested-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>

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