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SubjectRe: [PATCH 14/14] arm64: Add ARM_SMCCC_ARCH_WORKAROUND_1 BP hardening support
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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.

I'll have a look at it.

> Also, adding some printks here reveals that this function is called 32
> times in total, i.e., 4 times per CPU on my Overdrive. This is with
> the patches applied onto v4.15-rc9, so perhaps the rework takes care
> of this?

There is some ugly explosion in the number of callbacks as all of the
various implementations all share the same capability number. We can
take a shortcut and do an MIDR check early instead of late though.

But Suzuki is also reworking some of this, so I'll have a check with him.

Thanks,

M.
--
Jazz is not dead. It just smells funny...

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