[PATCH v3] random: handle archrandom with multiple longs

["Jason A. Donenfeld" <Jason@zx2c4.com>]

The archrandom interface was originally designed for x86, which supplies
RDRAND/RDSEED for receiving random words into registers, resulting in
one function to generate an int and another to generate a long. However,
other architectures don't follow this.

On arm64, the SMCCC TRNG interface can return between 1 and 3 longs. On
s390, the CPACF TRNG interface can return arbitrary amounts, with 32
longs having the same cost as one. On UML, the os_getrandom() interface
can return arbitrary amounts.

So change the api signature to take a "max_longs" parameter designating
the maximum number of longs requested, and then return the number of
longs generated.

Since callers need to check this return value and loop anyway, each arch
implementation does not bother implementing its own loop to try again to
fill the maximum number of longs. Additionally, all existing callers
pass in a constant max_longs parameter. Taken together, these two things
mean that the codegen doesn't really change much for one-word-at-a-time
platforms, while performance is greatly improved on platforms such as
s390.

Cc: Will Deacon <will@kernel.org>
Cc: Alexander Gordeev <agordeev@linux.ibm.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Borislav Petkov <bp@suse.de>
Cc: Heiko Carstens <hca@linux.ibm.com>
Cc: Johannes Berg <johannes@sipsolutions.net>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Harald Freudenberger <freude@linux.ibm.com>
Acked-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
---
 arch/arm64/include/asm/archrandom.h   | 102 ++++++++++++--------------
 arch/arm64/kernel/kaslr.c             |   2 +-
 arch/powerpc/include/asm/archrandom.h |  30 ++------
 arch/powerpc/kvm/book3s_hv.c          |   2 +-
 arch/s390/include/asm/archrandom.h    |  29 ++------
 arch/um/include/asm/archrandom.h      |  21 ++----
 arch/x86/include/asm/archrandom.h     |  41 +----------
 arch/x86/kernel/espfix_64.c           |   2 +-
 drivers/char/random.c                 |  45 ++++++++----
 include/asm-generic/archrandom.h      |  18 +----
 include/linux/random.h                |  12 +--
 11 files changed, 116 insertions(+), 188 deletions(-)

diff --git a/arch/arm64/include/asm/archrandom.h b/arch/arm64/include/asm/archrandom.h
index c3b9fa56af67..109e2a4454be 100644
--- a/arch/arm64/include/asm/archrandom.h
+++ b/arch/arm64/include/asm/archrandom.h
@@ -58,7 +58,7 @@ static inline bool __arm64_rndrrs(unsigned long *v)
 	return ok;
 }
 
-static inline bool __must_check arch_get_random_long(unsigned long *v)
+static inline size_t __must_check arch_get_random_longs(unsigned long *v, size_t max_longs)
 {
 	/*
 	 * Only support the generic interface after we have detected
@@ -66,27 +66,15 @@ static inline bool __must_check arch_get_random_long(unsigned long *v)
 	 * cpufeature code and with potential scheduling between CPUs
 	 * with and without the feature.
 	 */
-	if (cpus_have_const_cap(ARM64_HAS_RNG) && __arm64_rndr(v))
-		return true;
-	return false;
+	if (max_longs && cpus_have_const_cap(ARM64_HAS_RNG) && __arm64_rndr(v))
+		return 1;
+	return 0;
 }
 
-static inline bool __must_check arch_get_random_int(unsigned int *v)
+static inline size_t __must_check arch_get_random_seed_longs(unsigned long *v, size_t max_longs)
 {
-	if (cpus_have_const_cap(ARM64_HAS_RNG)) {
-		unsigned long val;
-
-		if (__arm64_rndr(&val)) {
-			*v = val;
-			return true;
-		}
-	}
-	return false;
-}
-
-static inline bool __must_check arch_get_random_seed_long(unsigned long *v)
-{
-	struct arm_smccc_res res;
+	if (!max_longs)
+		return 0;
 
 	/*
 	 * We prefer the SMCCC call, since its semantics (return actual
@@ -95,10 +83,23 @@ static inline bool __must_check arch_get_random_seed_long(unsigned long *v)
 	 * (the output of a pseudo RNG freshly seeded by a TRNG).
 	 */
 	if (smccc_trng_available) {
-		arm_smccc_1_1_invoke(ARM_SMCCC_TRNG_RND64, 64, &res);
+		struct arm_smccc_res res;
+
+		max_longs = min_t(size_t, 3, max_longs);
+		arm_smccc_1_1_invoke(ARM_SMCCC_TRNG_RND64, max_longs * 64, &res);
 		if ((int)res.a0 >= 0) {
-			*v = res.a3;
-			return true;
+			switch (max_longs) {
+			case 3:
+				*v++ = res.a1;
+				fallthrough;
+			case 2:
+				*v++ = res.a2;
+				fallthrough;
+			case 1:
+				*v++ = res.a3;
+				break;
+			}
+			return max_longs;
 		}
 	}
 
@@ -108,32 +109,9 @@ static inline bool __must_check arch_get_random_seed_long(unsigned long *v)
 	 * enough to implement this API if no other entropy source exists.
 	 */
 	if (cpus_have_const_cap(ARM64_HAS_RNG) && __arm64_rndrrs(v))
-		return true;
+		return 1;
 
-	return false;
-}
-
-static inline bool __must_check arch_get_random_seed_int(unsigned int *v)
-{
-	struct arm_smccc_res res;
-	unsigned long val;
-
-	if (smccc_trng_available) {
-		arm_smccc_1_1_invoke(ARM_SMCCC_TRNG_RND64, 32, &res);
-		if ((int)res.a0 >= 0) {
-			*v = res.a3 & GENMASK(31, 0);
-			return true;
-		}
-	}
-
-	if (cpus_have_const_cap(ARM64_HAS_RNG)) {
-		if (__arm64_rndrrs(&val)) {
-			*v = val;
-			return true;
-		}
-	}
-
-	return false;
+	return 0;
 }
 
 static inline bool __init __early_cpu_has_rndr(void)
@@ -143,26 +121,40 @@ static inline bool __init __early_cpu_has_rndr(void)
 	return (ftr >> ID_AA64ISAR0_EL1_RNDR_SHIFT) & 0xf;
 }
 
-static inline bool __init __must_check
-arch_get_random_seed_long_early(unsigned long *v)
+static inline size_t __init __must_check
+arch_get_random_seed_longs_early(unsigned long *v, size_t max_longs)
 {
 	WARN_ON(system_state != SYSTEM_BOOTING);
 
+	if (!max_longs)
+		return 0;
+
 	if (smccc_trng_available) {
 		struct arm_smccc_res res;
 
-		arm_smccc_1_1_invoke(ARM_SMCCC_TRNG_RND64, 64, &res);
+		max_longs = min_t(size_t, 3, max_longs);
+		arm_smccc_1_1_invoke(ARM_SMCCC_TRNG_RND64, max_longs * 64, &res);
 		if ((int)res.a0 >= 0) {
-			*v = res.a3;
-			return true;
+			switch (max_longs) {
+			case 3:
+				*v++ = res.a1;
+				fallthrough;
+			case 2:
+				*v++ = res.a2;
+				fallthrough;
+			case 1:
+				*v++ = res.a3;
+				break;
+			}
+			return max_longs;
 		}
 	}
 
 	if (__early_cpu_has_rndr() && __arm64_rndr(v))
-		return true;
+		return 1;
 
-	return false;
+	return 0;
 }
-#define arch_get_random_seed_long_early arch_get_random_seed_long_early
+#define arch_get_random_seed_longs_early arch_get_random_seed_longs_early
 
 #endif /* _ASM_ARCHRANDOM_H */
diff --git a/arch/arm64/kernel/kaslr.c b/arch/arm64/kernel/kaslr.c
index 418b2bba1521..c5d541f358d3 100644
--- a/arch/arm64/kernel/kaslr.c
+++ b/arch/arm64/kernel/kaslr.c
@@ -106,7 +106,7 @@ u64 __init kaslr_early_init(void)
 	 * and supported.
 	 */
 
-	if (arch_get_random_seed_long_early(&raw))
+	if (arch_get_random_seed_longs_early(&raw, 1))
 		seed ^= raw;
 
 	if (!seed) {
diff --git a/arch/powerpc/include/asm/archrandom.h b/arch/powerpc/include/asm/archrandom.h
index 25ba65df6b1a..0e365c5b2396 100644
--- a/arch/powerpc/include/asm/archrandom.h
+++ b/arch/powerpc/include/asm/archrandom.h
@@ -4,34 +4,16 @@
 
 #include <asm/machdep.h>
 
-static inline bool __must_check arch_get_random_long(unsigned long *v)
+static inline size_t __must_check arch_get_random_longs(unsigned long *v, size_t max_longs)
 {
-	return false;
+	return 0;
 }
 
-static inline bool __must_check arch_get_random_int(unsigned int *v)
+static inline size_t __must_check arch_get_random_seed_longs(unsigned long *v, size_t max_longs)
 {
-	return false;
-}
-
-static inline bool __must_check arch_get_random_seed_long(unsigned long *v)
-{
-	if (ppc_md.get_random_seed)
-		return ppc_md.get_random_seed(v);
-
-	return false;
-}
-
-static inline bool __must_check arch_get_random_seed_int(unsigned int *v)
-{
-	unsigned long val;
-	bool rc;
-
-	rc = arch_get_random_seed_long(&val);
-	if (rc)
-		*v = val;
-
-	return rc;
+	if (max_longs && ppc_md.get_random_seed && ppc_md.get_random_seed(v))
+		return 1;
+	return 0;
 }
 
 #ifdef CONFIG_PPC_POWERNV
diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c
index e08fb3124dca..631062cde6b4 100644
--- a/arch/powerpc/kvm/book3s_hv.c
+++ b/arch/powerpc/kvm/book3s_hv.c
@@ -1207,7 +1207,7 @@ int kvmppc_pseries_do_hcall(struct kvm_vcpu *vcpu)
 		break;
 #endif
 	case H_RANDOM:
-		if (!arch_get_random_seed_long(&vcpu->arch.regs.gpr[4]))
+		if (!arch_get_random_seed_longs(&vcpu->arch.regs.gpr[4], 1))
 			ret = H_HARDWARE;
 		break;
 	case H_RPT_INVALIDATE:
diff --git a/arch/s390/include/asm/archrandom.h b/arch/s390/include/asm/archrandom.h
index 0a1c2e66c709..cf5e000df0a1 100644
--- a/arch/s390/include/asm/archrandom.h
+++ b/arch/s390/include/asm/archrandom.h
@@ -18,34 +18,19 @@
 DECLARE_STATIC_KEY_FALSE(s390_arch_random_available);
 extern atomic64_t s390_arch_random_counter;
 
-static inline bool __must_check arch_get_random_long(unsigned long *v)
+static inline size_t __must_check arch_get_random_longs(unsigned long *v, size_t max_longs)
 {
-	return false;
+	return 0;
 }
 
-static inline bool __must_check arch_get_random_int(unsigned int *v)
-{
-	return false;
-}
-
-static inline bool __must_check arch_get_random_seed_long(unsigned long *v)
-{
-	if (static_branch_likely(&s390_arch_random_available)) {
-		cpacf_trng(NULL, 0, (u8 *)v, sizeof(*v));
-		atomic64_add(sizeof(*v), &s390_arch_random_counter);
-		return true;
-	}
-	return false;
-}
-
-static inline bool __must_check arch_get_random_seed_int(unsigned int *v)
+static inline size_t __must_check arch_get_random_seed_longs(unsigned long *v, size_t max_longs)
 {
 	if (static_branch_likely(&s390_arch_random_available)) {
-		cpacf_trng(NULL, 0, (u8 *)v, sizeof(*v));
-		atomic64_add(sizeof(*v), &s390_arch_random_counter);
-		return true;
+		cpacf_trng(NULL, 0, (u8 *)v, max_longs * sizeof(*v));
+		atomic64_add(max_longs * sizeof(*v), &s390_arch_random_counter);
+		return max_longs;
 	}
-	return false;
+	return 0;
 }
 
 #endif /* _ASM_S390_ARCHRANDOM_H */
diff --git a/arch/um/include/asm/archrandom.h b/arch/um/include/asm/archrandom.h
index 2f24cb96391d..24e16c979c51 100644
--- a/arch/um/include/asm/archrandom.h
+++ b/arch/um/include/asm/archrandom.h
@@ -7,24 +7,19 @@
 /* This is from <os.h>, but better not to #include that in a global header here. */
 ssize_t os_getrandom(void *buf, size_t len, unsigned int flags);
 
-static inline bool __must_check arch_get_random_long(unsigned long *v)
+static inline size_t __must_check arch_get_random_longs(unsigned long *v, size_t max_longs)
 {
-	return os_getrandom(v, sizeof(*v), 0) == sizeof(*v);
-}
+	ssize_t ret;
 
-static inline bool __must_check arch_get_random_int(unsigned int *v)
-{
-	return os_getrandom(v, sizeof(*v), 0) == sizeof(*v);
-}
-
-static inline bool __must_check arch_get_random_seed_long(unsigned long *v)
-{
-	return false;
+	ret = os_getrandom(v, max_longs * sizeof(*v), 0);
+	if (ret < 0)
+		return 0;
+	return ret / sizeof(*v);
 }
 
-static inline bool __must_check arch_get_random_seed_int(unsigned int *v)
+static inline size_t __must_check arch_get_random_seed_longs(unsigned long *v, size_t max_longs)
 {
-	return false;
+	return 0;
 }
 
 #endif
diff --git a/arch/x86/include/asm/archrandom.h b/arch/x86/include/asm/archrandom.h
index fb235b696175..02bae8e0758b 100644
--- a/arch/x86/include/asm/archrandom.h
+++ b/arch/x86/include/asm/archrandom.h
@@ -31,20 +31,6 @@ static inline bool __must_check rdrand_long(unsigned long *v)
 	return false;
 }
 
-static inline bool __must_check rdrand_int(unsigned int *v)
-{
-	bool ok;
-	unsigned int retry = RDRAND_RETRY_LOOPS;
-	do {
-		asm volatile("rdrand %[out]"
-			     CC_SET(c)
-			     : CC_OUT(c) (ok), [out] "=r" (*v));
-		if (ok)
-			return true;
-	} while (--retry);
-	return false;
-}
-
 static inline bool __must_check rdseed_long(unsigned long *v)
 {
 	bool ok;
@@ -54,38 +40,19 @@ static inline bool __must_check rdseed_long(unsigned long *v)
 	return ok;
 }
 
-static inline bool __must_check rdseed_int(unsigned int *v)
-{
-	bool ok;
-	asm volatile("rdseed %[out]"
-		     CC_SET(c)
-		     : CC_OUT(c) (ok), [out] "=r" (*v));
-	return ok;
-}
-
 /*
  * These are the generic interfaces; they must not be declared if the
  * stubs in <linux/random.h> are to be invoked.
  */
 
-static inline bool __must_check arch_get_random_long(unsigned long *v)
-{
-	return static_cpu_has(X86_FEATURE_RDRAND) ? rdrand_long(v) : false;
-}
-
-static inline bool __must_check arch_get_random_int(unsigned int *v)
-{
-	return static_cpu_has(X86_FEATURE_RDRAND) ? rdrand_int(v) : false;
-}
-
-static inline bool __must_check arch_get_random_seed_long(unsigned long *v)
+static inline size_t __must_check arch_get_random_longs(unsigned long *v, size_t max_longs)
 {
-	return static_cpu_has(X86_FEATURE_RDSEED) ? rdseed_long(v) : false;
+	return max_longs && static_cpu_has(X86_FEATURE_RDRAND) && rdrand_long(v) ? 1 : 0;
 }
 
-static inline bool __must_check arch_get_random_seed_int(unsigned int *v)
+static inline size_t __must_check arch_get_random_seed_longs(unsigned long *v, size_t max_longs)
 {
-	return static_cpu_has(X86_FEATURE_RDSEED) ? rdseed_int(v) : false;
+	return max_longs && static_cpu_has(X86_FEATURE_RDSEED) && rdseed_long(v) ? 1 : 0;
 }
 
 #ifndef CONFIG_UML
diff --git a/arch/x86/kernel/espfix_64.c b/arch/x86/kernel/espfix_64.c
index 4fe7af58cfe1..9417d5aa7305 100644
--- a/arch/x86/kernel/espfix_64.c
+++ b/arch/x86/kernel/espfix_64.c
@@ -100,7 +100,7 @@ static void init_espfix_random(void)
 	 * This is run before the entropy pools are initialized,
 	 * but this is hopefully better than nothing.
 	 */
-	if (!arch_get_random_long(&rand)) {
+	if (!arch_get_random_longs(&rand, 1)) {
 		/* The constant is an arbitrary large prime */
 		rand = rdtsc();
 		rand *= 0xc345c6b72fd16123UL;
diff --git a/drivers/char/random.c b/drivers/char/random.c
index 0c6568ae5f68..7bf11fa66265 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -596,12 +596,20 @@ static void extract_entropy(void *buf, size_t len)
 		unsigned long rdseed[32 / sizeof(long)];
 		size_t counter;
 	} block;
-	size_t i;
+	size_t i, longs;
 
-	for (i = 0; i < ARRAY_SIZE(block.rdseed); ++i) {
-		if (!arch_get_random_seed_long(&block.rdseed[i]) &&
-		    !arch_get_random_long(&block.rdseed[i]))
-			block.rdseed[i] = random_get_entropy();
+	for (i = 0; i < ARRAY_SIZE(block.rdseed);) {
+		longs = arch_get_random_seed_longs(&block.rdseed[i], ARRAY_SIZE(block.rdseed) - i);
+		if (longs) {
+			i += longs;
+			continue;
+		}
+		longs = arch_get_random_longs(&block.rdseed[i], ARRAY_SIZE(block.rdseed) - i);
+		if (longs) {
+			i += longs;
+			continue;
+		}
+		block.rdseed[i++] = random_get_entropy();
 	}
 
 	spin_lock_irqsave(&input_pool.lock, flags);
@@ -776,22 +784,31 @@ static struct notifier_block pm_notifier = { .notifier_call = random_pm_notifica
 int __init random_init(const char *command_line)
 {
 	ktime_t now = ktime_get_real();
-	unsigned int i, arch_bits;
-	unsigned long entropy;
+	size_t i, longs, arch_bits;
+	unsigned long entropy[BLAKE2S_BLOCK_SIZE / sizeof(long)];
 
 #if defined(LATENT_ENTROPY_PLUGIN)
 	static const u8 compiletime_seed[BLAKE2S_BLOCK_SIZE] __initconst __latent_entropy;
 	_mix_pool_bytes(compiletime_seed, sizeof(compiletime_seed));
 #endif
 
-	for (i = 0, arch_bits = BLAKE2S_BLOCK_SIZE * 8;
-	     i < BLAKE2S_BLOCK_SIZE; i += sizeof(entropy)) {
-		if (!arch_get_random_seed_long_early(&entropy) &&
-		    !arch_get_random_long_early(&entropy)) {
-			entropy = random_get_entropy();
-			arch_bits -= sizeof(entropy) * 8;
+	for (i = 0, arch_bits = sizeof(entropy) * 8; i < ARRAY_SIZE(entropy);) {
+		longs = arch_get_random_seed_longs(entropy, ARRAY_SIZE(entropy) - i);
+		if (longs) {
+			_mix_pool_bytes(entropy, sizeof(*entropy) * longs);
+			i += longs;
+			continue;
 		}
-		_mix_pool_bytes(&entropy, sizeof(entropy));
+		longs = arch_get_random_longs(entropy, ARRAY_SIZE(entropy) - i);
+		if (longs) {
+			_mix_pool_bytes(entropy, sizeof(*entropy) * longs);
+			i += longs;
+			continue;
+		}
+		entropy[0] = random_get_entropy();
+		_mix_pool_bytes(entropy, sizeof(*entropy));
+		arch_bits -= sizeof(*entropy) * 8;
+		++i;
 	}
 	_mix_pool_bytes(&now, sizeof(now));
 	_mix_pool_bytes(utsname(), sizeof(*(utsname())));
diff --git a/include/asm-generic/archrandom.h b/include/asm-generic/archrandom.h
index 3a5ee202dd86..3cd7f980cfdc 100644
--- a/include/asm-generic/archrandom.h
+++ b/include/asm-generic/archrandom.h
@@ -2,24 +2,14 @@
 #ifndef __ASM_GENERIC_ARCHRANDOM_H__
 #define __ASM_GENERIC_ARCHRANDOM_H__
 
-static inline bool __must_check arch_get_random_long(unsigned long *v)
+static inline size_t __must_check arch_get_random_longs(unsigned long *v, size_t max_longs)
 {
-	return false;
+	return 0;
 }
 
-static inline bool __must_check arch_get_random_int(unsigned int *v)
+static inline size_t __must_check arch_get_random_seed_longs(unsigned long *v, size_t max_longs)
 {
-	return false;
-}
-
-static inline bool __must_check arch_get_random_seed_long(unsigned long *v)
-{
-	return false;
-}
-
-static inline bool __must_check arch_get_random_seed_int(unsigned int *v)
-{
-	return false;
+	return 0;
 }
 
 #endif
diff --git a/include/linux/random.h b/include/linux/random.h
index 865770e29f3e..3fec206487f6 100644
--- a/include/linux/random.h
+++ b/include/linux/random.h
@@ -112,19 +112,19 @@ declare_get_random_var_wait(long, unsigned long)
  * Called from the boot CPU during startup; not valid to call once
  * secondary CPUs are up and preemption is possible.
  */
-#ifndef arch_get_random_seed_long_early
-static inline bool __init arch_get_random_seed_long_early(unsigned long *v)
+#ifndef arch_get_random_seed_longs_early
+static inline size_t __init arch_get_random_seed_longs_early(unsigned long *v, size_t max_longs)
 {
 	WARN_ON(system_state != SYSTEM_BOOTING);
-	return arch_get_random_seed_long(v);
+	return arch_get_random_seed_longs(v, max_longs);
 }
 #endif
 
-#ifndef arch_get_random_long_early
-static inline bool __init arch_get_random_long_early(unsigned long *v)
+#ifndef arch_get_random_longs_early
+static inline bool __init arch_get_random_longs_early(unsigned long *v, size_t max_longs)
 {
 	WARN_ON(system_state != SYSTEM_BOOTING);
-	return arch_get_random_long(v);
+	return arch_get_random_longs(v, max_longs);
 }
 #endif
 
-- 
2.35.1