SMCCCv1.3 added a hint bit which callers can set in an SMCCC function ID (AKA "FID") to indicate that it is acceptable for the SMCCC implementation to discard SVE and/or SME state over a specific SMCCC call. The kernel support for using this hint is broken and SMCCC calls may clobber the SVE and/or SME state of arbitrary tasks, though FPSIMD state is unaffected.

The kernel support is intended to use the hint when there is no SVE or SME state to save, and to do this it checks whether TIF_FOREIGN_FPSTATE is set or TIF_SVE is clear in assembly code:

| ldr <flags>, [<current_task>, #TSK_TI_FLAGS] | tbnz <flags>, #TIF_FOREIGN_FPSTATE, 1f // Any live FP state? | tbnz <flags>, #TIF_SVE, 2f // Does that state include SVE? | | 1: orr <fid>, <fid>, ARM_SMCCC_1_3_SVE_HINT | 2: | << SMCCC call using FID >>

This is not safe as-is:

(1) SMCCC calls can be made in a preemptible context and preemption can result in TIF_FOREIGN_FPSTATE being set or cleared at arbitrary points in time. Thus checking for TIF_FOREIGN_FPSTATE provides no guarantee.

(2) TIF_FOREIGN_FPSTATE only indicates that the live FP/SVE/SME state in the CPU does not belong to the current task, and does not indicate that clobbering this state is acceptable.

When the live CPU state is clobbered it is necessary to update fpsimd_last_state.st to ensure that a subsequent context switch will reload FP/SVE/SME state from memory rather than consuming the clobbered state. This and the SMCCC call itself must happen in a critical section with preemption disabled to avoid races.

(3) Live SVE/SME state can exist with TIF_SVE clear (e.g. with only TIF_SME set), and checking TIF_SVE alone is insufficient.

Remove the broken support for the SMCCCv1.3 SVE saving hint. This is effectively a revert of commits:

* cfa7ff959a789a95 ("arm64: smccc: Support SMCCC v1.3 SVE register saving hint") * a7c3acca53801e10 ("arm64: smccc: Save lr before calling __arm_smccc_sve_check()")

... leaving behind the ARM_SMCCC_VERSION_1_3 and ARM_SMCCC_1_3_SVE_HINT definitions, since these are simply definitions from the SMCCC specification, and the latter is used in KVM via ARM_SMCCC_CALL_HINTS.

If we want to bring this back in future, we'll probably want to handle this logic in C where we can use all the usual FPSIMD/SVE/SME helper functions, and that'll likely require some rework of the SMCCC code and/or its callers.

Fixes: cfa7ff959a789a95 ("arm64: smccc: Support SMCCC v1.3 SVE register saving hint") Signed-off-by: Mark Rutland mark.rutland@arm.com Cc: Ard Biesheuvel ardb@kernel.org Cc: Catalin Marinas catalin.marinas@arm.com Cc: Marc Zyngier maz@kernel.org Cc: Mark Brown broonie@kernel.org Cc: Will Deacon will@kernel.org Cc: stable@vger.kernel.org --- arch/arm64/kernel/smccc-call.S | 35 +++------------------------------- drivers/firmware/smccc/smccc.c | 4 ---- include/linux/arm-smccc.h | 32 +++---------------------------- 3 files changed, 6 insertions(+), 65 deletions(-)

diff --git a/arch/arm64/kernel/smccc-call.S b/arch/arm64/kernel/smccc-call.S index 487381164ff6b..2def9d0dd3ddb 100644 --- a/arch/arm64/kernel/smccc-call.S +++ b/arch/arm64/kernel/smccc-call.S @@ -7,48 +7,19 @@

#include <asm/asm-offsets.h> #include <asm/assembler.h> -#include <asm/thread_info.h> - -/* - * If we have SMCCC v1.3 and (as is likely) no SVE state in - * the registers then set the SMCCC hint bit to say there's no - * need to preserve it. Do this by directly adjusting the SMCCC - * function value which is already stored in x0 ready to be called. - */ -SYM_FUNC_START(__arm_smccc_sve_check) - - ldr_l x16, smccc_has_sve_hint - cbz x16, 2f - - get_current_task x16 - ldr x16, [x16, #TSK_TI_FLAGS] - tbnz x16, #TIF_FOREIGN_FPSTATE, 1f // Any live FP state? - tbnz x16, #TIF_SVE, 2f // Does that state include SVE? - -1: orr x0, x0, ARM_SMCCC_1_3_SVE_HINT - -2: ret -SYM_FUNC_END(__arm_smccc_sve_check) -EXPORT_SYMBOL(__arm_smccc_sve_check)

.macro SMCCC instr - stp x29, x30, [sp, #-16]! - mov x29, sp -alternative_if ARM64_SVE - bl __arm_smccc_sve_check -alternative_else_nop_endif \instr #0 - ldr x4, [sp, #16] + ldr x4, [sp] stp x0, x1, [x4, #ARM_SMCCC_RES_X0_OFFS] stp x2, x3, [x4, #ARM_SMCCC_RES_X2_OFFS] - ldr x4, [sp, #24] + ldr x4, [sp, #8] cbz x4, 1f /* no quirk structure */ ldr x9, [x4, #ARM_SMCCC_QUIRK_ID_OFFS] cmp x9, #ARM_SMCCC_QUIRK_QCOM_A6 b.ne 1f str x6, [x4, ARM_SMCCC_QUIRK_STATE_OFFS] -1: ldp x29, x30, [sp], #16 - ret +1: ret .endm

/* diff --git a/drivers/firmware/smccc/smccc.c b/drivers/firmware/smccc/smccc.c index d670635914ecb..a74600d9f2d72 100644 --- a/drivers/firmware/smccc/smccc.c +++ b/drivers/firmware/smccc/smccc.c @@ -16,7 +16,6 @@ static u32 smccc_version = ARM_SMCCC_VERSION_1_0; static enum arm_smccc_conduit smccc_conduit = SMCCC_CONDUIT_NONE;

bool __ro_after_init smccc_trng_available = false; -u64 __ro_after_init smccc_has_sve_hint = false; s32 __ro_after_init smccc_soc_id_version = SMCCC_RET_NOT_SUPPORTED; s32 __ro_after_init smccc_soc_id_revision = SMCCC_RET_NOT_SUPPORTED;

@@ -28,9 +27,6 @@ void __init arm_smccc_version_init(u32 version, enum arm_smccc_conduit conduit) smccc_conduit = conduit;

smccc_trng_available = smccc_probe_trng(); - if (IS_ENABLED(CONFIG_ARM64_SVE) && - smccc_version >= ARM_SMCCC_VERSION_1_3) - smccc_has_sve_hint = true;

if ((smccc_version >= ARM_SMCCC_VERSION_1_2) && (smccc_conduit != SMCCC_CONDUIT_NONE)) { diff --git a/include/linux/arm-smccc.h b/include/linux/arm-smccc.h index f59099a213d0d..67f6fdf2e7cd8 100644 --- a/include/linux/arm-smccc.h +++ b/include/linux/arm-smccc.h @@ -315,8 +315,6 @@ u32 arm_smccc_get_version(void);

void __init arm_smccc_version_init(u32 version, enum arm_smccc_conduit conduit);

-extern u64 smccc_has_sve_hint; - /** * arm_smccc_get_soc_id_version() * @@ -414,15 +412,6 @@ struct arm_smccc_quirk { } state; };

-/** - * __arm_smccc_sve_check() - Set the SVE hint bit when doing SMC calls - * - * Sets the SMCCC hint bit to indicate if there is live state in the SVE - * registers, this modifies x0 in place and should never be called from C - * code. - */ -asmlinkage unsigned long __arm_smccc_sve_check(unsigned long x0); - /** * __arm_smccc_smc() - make SMC calls * @a0-a7: arguments passed in registers 0 to 7 @@ -490,20 +479,6 @@ asmlinkage void __arm_smccc_hvc(unsigned long a0, unsigned long a1,

#endif

-/* nVHE hypervisor doesn't have a current thread so needs separate checks */ -#if defined(CONFIG_ARM64_SVE) && !defined(__KVM_NVHE_HYPERVISOR__) - -#define SMCCC_SVE_CHECK ALTERNATIVE("nop \n", "bl __arm_smccc_sve_check \n", \ - ARM64_SVE) -#define smccc_sve_clobbers "x16", "x30", "cc", - -#else - -#define SMCCC_SVE_CHECK -#define smccc_sve_clobbers - -#endif - #define __constraint_read_2 "r" (arg0) #define __constraint_read_3 __constraint_read_2, "r" (arg1) #define __constraint_read_4 __constraint_read_3, "r" (arg2) @@ -574,12 +549,11 @@ asmlinkage void __arm_smccc_hvc(unsigned long a0, unsigned long a1, register unsigned long r3 asm("r3"); \ CONCATENATE(__declare_arg_, \ COUNT_ARGS(__VA_ARGS__))(__VA_ARGS__); \ - asm volatile(SMCCC_SVE_CHECK \ - inst "\n" : \ + asm volatile(inst "\n" : \ "=r" (r0), "=r" (r1), "=r" (r2), "=r" (r3) \ : CONCATENATE(__constraint_read_, \ COUNT_ARGS(__VA_ARGS__)) \ - : smccc_sve_clobbers "memory"); \ + : "memory"); \ if (___res) \ *___res = (typeof(*___res)){r0, r1, r2, r3}; \ } while (0) @@ -628,7 +602,7 @@ asmlinkage void __arm_smccc_hvc(unsigned long a0, unsigned long a1, asm ("" : \ : CONCATENATE(__constraint_read_, \ COUNT_ARGS(__VA_ARGS__)) \ - : smccc_sve_clobbers "memory"); \ + : "memory"); \ if (___res) \ ___res->a0 = SMCCC_RET_NOT_SUPPORTED; \ } while (0)