[PATCH v6 0/1] arm64: Implement archrandom.h for ARMv8.5-RNG

[PATCH v6 0/1] arm64: Implement archrandom.h for ARMv8.5-RNG

[richard.henderson]

From: Richard Henderson <richard.henderson@linaro.org>

Here's v6.  I believe I've collected all of the comments
from both Ard and Mark across v4 and v5, as well as from
the cafe in Lyon.

I had thought about using a simple function pointer for
arch_get_random_seed_long, but didn't see a good place
where I could update that at the end of boot.

Which lead me to ALTERNATIVE_CB, which is way overkill,
but is already part of the update infrastructure.

Tested with qemu -cpu {max,cortex-a57}, which covers both
sides of the alternative.  GDB breakpoints confirm that
boot_get_random_seed_long is what is called from rand_initialize,
and that this_cpu_has_cap returns the correct result.


r~


 Documentation/arm64/cpu-feature-registers.rst |  2 +
 arch/arm64/include/asm/archrandom.h           | 55 +++++++++++++++
 arch/arm64/include/asm/cpucaps.h              |  3 +-
 arch/arm64/include/asm/sysreg.h               |  4 ++
 arch/arm64/kernel/cpufeature.c                | 13 ++++
 arch/arm64/kernel/random.c                    | 67 +++++++++++++++++++
 arch/arm64/Kconfig                            | 12 ++++
 arch/arm64/kernel/Makefile                    |  1 +
 drivers/char/Kconfig                          |  4 +-
 9 files changed, 158 insertions(+), 3 deletions(-)
 create mode 100644 arch/arm64/include/asm/archrandom.h
 create mode 100644 arch/arm64/kernel/random.c

-- 
2.17.1

[PATCH v6 1/1] arm64: Implement archrandom.h for ARMv8.5-RNG

[richard.henderson]

From: Richard Henderson <richard.henderson@linaro.org>

Expose the ID_AA64ISAR0.RNDR field to userspace, as the
RNG system registers are always available at EL0.

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
---
v2: Use __mrs_s and fix missing cc clobber (Mark),
    Log rng failures with pr_warn (Mark),
    Use __must_check; put RNDR in arch_get_random_long and RNDRRS
    in arch_get_random_seed_long (Ard),
    Use ARM64_CPUCAP_WEAK_LOCAL_CPU_FEATURE, and check this_cpu_has_cap
    when reading random data.  Move everything out of line, now that
    there are 5 other function calls involved, and to unify the rate
    limiting on the pr_warn.
v3: Keep arch_get_random{,_seed}_long in sync.
v4: Use __cpus_have_const_cap before falling back to this_cpu_has_cap.
v5: Improve commentary; fix some checkpatch warnings.
v6: Drop arch_get_random_long, use RNDR in arch_get_random_seed_long,
    do not use RNDRRS at all (Ard).
    Drop the pr_warn mis-communication (Mark).
    Use ARM64_CPUCAP_SYSTEM_FEATURE for feature detection (Mark).
    Move arch_get_random_seed_long back inline using ALTERNATIVE_CB.
---
 Documentation/arm64/cpu-feature-registers.rst |  2 +
 arch/arm64/include/asm/archrandom.h           | 55 +++++++++++++++
 arch/arm64/include/asm/cpucaps.h              |  3 +-
 arch/arm64/include/asm/sysreg.h               |  4 ++
 arch/arm64/kernel/cpufeature.c                | 13 ++++
 arch/arm64/kernel/random.c                    | 67 +++++++++++++++++++
 arch/arm64/Kconfig                            | 12 ++++
 arch/arm64/kernel/Makefile                    |  1 +
 drivers/char/Kconfig                          |  4 +-
 9 files changed, 158 insertions(+), 3 deletions(-)
 create mode 100644 arch/arm64/include/asm/archrandom.h
 create mode 100644 arch/arm64/kernel/random.c

diff --git a/Documentation/arm64/cpu-feature-registers.rst b/Documentation/arm64/cpu-feature-registers.rst
index 2955287e9acc..78d6f5c6e824 100644
--- a/Documentation/arm64/cpu-feature-registers.rst
+++ b/Documentation/arm64/cpu-feature-registers.rst
@@ -117,6 +117,8 @@ infrastructure:
      +------------------------------+---------+---------+
      | Name                         |  bits   | visible |
      +------------------------------+---------+---------+
+     | RNDR                         | [63-60] |    y    |
+     +------------------------------+---------+---------+
      | TS                           | [55-52] |    y    |
      +------------------------------+---------+---------+
      | FHM                          | [51-48] |    y    |
diff --git a/arch/arm64/include/asm/archrandom.h b/arch/arm64/include/asm/archrandom.h
new file mode 100644
index 000000000000..7b9f397d2a54
--- /dev/null
+++ b/arch/arm64/include/asm/archrandom.h
@@ -0,0 +1,55 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _ASM_ARCHRANDOM_H
+#define _ASM_ARCHRANDOM_H
+
+#ifdef CONFIG_ARCH_RANDOM
+
+#include <asm/alternative.h>
+
+void arm64_update_get_random_seed_long(struct alt_instr *alt,
+				       __le32 *origptr, __le32 *updptr,
+				       int nr_inst);
+
+static inline bool __must_check arch_get_random_long(unsigned long *v)
+{
+	return false;
+}
+
+static inline bool __must_check arch_get_random_int(unsigned int *v)
+{
+	return false;
+}
+
+/*
+ * The ALTERNATIVE infrastructure leads GCC to believe that the
+ * inline assembly is quite large, rather than two insns, which
+ * leads to the function being considered not profitable to inline.
+ * Override this decision with __always_inline.
+ */
+static __always_inline __must_check
+bool arch_get_random_seed_long(unsigned long *v)
+{
+	register unsigned long x0 __asm__("x0");
+	unsigned long ok;
+
+	asm volatile(ALTERNATIVE_CB("bl boot_get_random_seed_long\n",
+				    arm64_update_get_random_seed_long)
+		     "cset %1, ne\n"
+		     : "=r" (x0), "=r" (ok) : : "cc");
+
+	*v = x0;
+	return ok;
+}
+
+static __always_inline __must_check
+bool arch_get_random_seed_int(unsigned int *v)
+{
+	unsigned long val;
+	bool ok = arch_get_random_seed_long(&val);
+
+	*v = val;
+	return ok;
+}
+
+#endif /* CONFIG_ARCH_RANDOM */
+#endif /* _ASM_ARCHRANDOM_H */
diff --git a/arch/arm64/include/asm/cpucaps.h b/arch/arm64/include/asm/cpucaps.h
index ac1dbca3d0cd..1dd7644bc59a 100644
--- a/arch/arm64/include/asm/cpucaps.h
+++ b/arch/arm64/include/asm/cpucaps.h
@@ -54,7 +54,8 @@
 #define ARM64_WORKAROUND_1463225		44
 #define ARM64_WORKAROUND_CAVIUM_TX2_219_TVM	45
 #define ARM64_WORKAROUND_CAVIUM_TX2_219_PRFM	46
+#define ARM64_HAS_RNG				47
 
-#define ARM64_NCAPS				47
+#define ARM64_NCAPS				48
 
 #endif /* __ASM_CPUCAPS_H */
diff --git a/arch/arm64/include/asm/sysreg.h b/arch/arm64/include/asm/sysreg.h
index 6e919fafb43d..5e718f279469 100644
--- a/arch/arm64/include/asm/sysreg.h
+++ b/arch/arm64/include/asm/sysreg.h
@@ -365,6 +365,9 @@
 #define SYS_CTR_EL0			sys_reg(3, 3, 0, 0, 1)
 #define SYS_DCZID_EL0			sys_reg(3, 3, 0, 0, 7)
 
+#define SYS_RNDR_EL0			sys_reg(3, 3, 2, 4, 0)
+#define SYS_RNDRRS_EL0			sys_reg(3, 3, 2, 4, 1)
+
 #define SYS_PMCR_EL0			sys_reg(3, 3, 9, 12, 0)
 #define SYS_PMCNTENSET_EL0		sys_reg(3, 3, 9, 12, 1)
 #define SYS_PMCNTENCLR_EL0		sys_reg(3, 3, 9, 12, 2)
@@ -539,6 +542,7 @@
 			 ENDIAN_SET_EL1 | SCTLR_EL1_UCI  | SCTLR_EL1_RES1)
 
 /* id_aa64isar0 */
+#define ID_AA64ISAR0_RNDR_SHIFT		60
 #define ID_AA64ISAR0_TS_SHIFT		52
 #define ID_AA64ISAR0_FHM_SHIFT		48
 #define ID_AA64ISAR0_DP_SHIFT		44
diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index 80f459ad0190..8c3be148c3a2 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -119,6 +119,7 @@ static void cpu_enable_cnp(struct arm64_cpu_capabilities const *cap);
  * sync with the documentation of the CPU feature register ABI.
  */
 static const struct arm64_ftr_bits ftr_id_aa64isar0[] = {
+	ARM64_FTR_BITS(FTR_VISIBLE, FTR_STRICT, FTR_LOWER_SAFE, ID_AA64ISAR0_RNDR_SHIFT, 4, 0),
 	ARM64_FTR_BITS(FTR_VISIBLE, FTR_STRICT, FTR_LOWER_SAFE, ID_AA64ISAR0_TS_SHIFT, 4, 0),
 	ARM64_FTR_BITS(FTR_VISIBLE, FTR_STRICT, FTR_LOWER_SAFE, ID_AA64ISAR0_FHM_SHIFT, 4, 0),
 	ARM64_FTR_BITS(FTR_VISIBLE, FTR_STRICT, FTR_LOWER_SAFE, ID_AA64ISAR0_DP_SHIFT, 4, 0),
@@ -1565,6 +1566,18 @@ static const struct arm64_cpu_capabilities arm64_features[] = {
 		.sign = FTR_UNSIGNED,
 		.min_field_value = 1,
 	},
+#endif
+#ifdef CONFIG_ARCH_RANDOM
+	{
+		.desc = "Random Number Generator",
+		.capability = ARM64_HAS_RNG,
+		.type = ARM64_CPUCAP_SYSTEM_FEATURE,
+		.matches = has_cpuid_feature,
+		.sys_reg = SYS_ID_AA64ISAR0_EL1,
+		.field_pos = ID_AA64ISAR0_RNDR_SHIFT,
+		.sign = FTR_UNSIGNED,
+		.min_field_value = 1,
+	},
 #endif
 	{},
 };
diff --git a/arch/arm64/kernel/random.c b/arch/arm64/kernel/random.c
new file mode 100644
index 000000000000..04c65445c43f
--- /dev/null
+++ b/arch/arm64/kernel/random.c
@@ -0,0 +1,67 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Random number generation using ARMv8.5-RNG.
+ */
+
+#include <linux/random.h>
+#include <linux/ratelimit.h>
+#include <linux/printk.h>
+#include <linux/preempt.h>
+#include <asm/cpufeature.h>
+
+/*
+ * Before alternatives are finalized, arch_get_random_seed_long calls
+ * this function.  The abi is as if
+ *
+ *     msr x0, rndr
+ *
+ * Preserve all other call-clobbered regs.
+ */
+
+asm(".globl	boot_get_random_seed_long\n"
+".type	boot_get_random_seed_long, @function\n"
+"boot_get_random_seed_long:\n"
+"	stp	x29, x30, [sp, -160]!\n"
+"	stp	x1, x2, [sp, 16]\n"
+"	stp	x3, x4, [sp, 32]\n"
+"	stp	x5, x6, [sp, 48]\n"
+"	stp	x7, x8, [sp, 64]\n"
+"	stp	x9, x10, [sp, 80]\n"
+"	stp	x11, x12, [sp, 96]\n"
+"	stp	x13, x14, [sp, 112]\n"
+"	stp	x15, x16, [sp, 128]\n"
+"	stp	x17, x18, [sp, 144]\n"
+"	mov	x0, " __stringify(ARM64_HAS_RNG) "\n"
+"	bl	this_cpu_has_cap\n"
+"	ldp	x1, x2, [sp, 16]\n"
+"	ldp	x3, x4, [sp, 32]\n"
+"	ldp	x5, x6, [sp, 48]\n"
+"	ldp	x7, x8, [sp, 64]\n"
+"	ldp	x9, x10, [sp, 80]\n"
+"	ldp	x11, x12, [sp, 96]\n"
+"	ldp	x13, x14, [sp, 112]\n"
+"	ldp	x15, x16, [sp, 128]\n"
+"	ldp	x17, x18, [sp, 144]\n"
+"	ldp	x29, x30, [sp], 160\n"
+/* Test this_cpu_has_cap result, clearing x0 and setting Z if false. */
+"	ands	w0, w0, #0xff\n"
+"	beq	1f\n"
+	__mrs_s("x0", SYS_RNDR_EL0) "\n"
+"1:	ret\n"
+".size boot_get_random_seed_long, . - boot_get_random_seed_long\n");
+
+
+void arm64_update_get_random_seed_long(struct alt_instr *alt,
+				       __le32 *origptr, __le32 *updptr,
+				       int nr_inst)
+{
+	u32 insn;
+
+	BUG_ON(nr_inst != 1);
+
+	if (cpus_have_cap(ARM64_HAS_RNG))
+		insn = 0xd53b2400;	/* mrs	x0, rndr */
+	else
+		insn = 0xea1f03e0;	/* ands	x0, xzr, xzr */
+	updptr[0] = cpu_to_le32(insn);
+}
diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index 3f047afb982c..5bc88601f07b 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -1438,6 +1438,18 @@ config ARM64_PTR_AUTH
 
 endmenu
 
+menu "ARMv8.5 architectural features"
+
+config ARCH_RANDOM
+	bool "Enable support for random number generation"
+	default y
+	help
+	  Random number generation (part of the ARMv8.5 Extensions)
+	  provides a high bandwidth, cryptographically secure
+	  hardware random number generator.
+
+endmenu
+
 config ARM64_SVE
 	bool "ARM Scalable Vector Extension support"
 	default y
diff --git a/arch/arm64/kernel/Makefile b/arch/arm64/kernel/Makefile
index 478491f07b4f..a47c2b984da7 100644
--- a/arch/arm64/kernel/Makefile
+++ b/arch/arm64/kernel/Makefile
@@ -63,6 +63,7 @@ obj-$(CONFIG_CRASH_CORE)		+= crash_core.o
 obj-$(CONFIG_ARM_SDE_INTERFACE)		+= sdei.o
 obj-$(CONFIG_ARM64_SSBD)		+= ssbd.o
 obj-$(CONFIG_ARM64_PTR_AUTH)		+= pointer_auth.o
+obj-$(CONFIG_ARCH_RANDOM)		+= random.o
 
 obj-y					+= vdso/ probes/
 obj-$(CONFIG_COMPAT_VDSO)		+= vdso32/
diff --git a/drivers/char/Kconfig b/drivers/char/Kconfig
index df0fc997dc3e..f26a0a8cc0d0 100644
--- a/drivers/char/Kconfig
+++ b/drivers/char/Kconfig
@@ -539,7 +539,7 @@ endmenu
 
 config RANDOM_TRUST_CPU
 	bool "Trust the CPU manufacturer to initialize Linux's CRNG"
-	depends on X86 || S390 || PPC
+	depends on X86 || S390 || PPC || ARM64
 	default n
 	help
 	Assume that CPU manufacturer (e.g., Intel or AMD for RDSEED or
@@ -559,4 +559,4 @@ config RANDOM_TRUST_BOOTLOADER
 	device randomness. Say Y here to assume the entropy provided by the
 	booloader is trustworthy so it will be added to the kernel's entropy
 	pool. Otherwise, say N here so it will be regarded as device input that
-	only mixes the entropy pool.
\ No newline at end of file
+	only mixes the entropy pool.
-- 
2.17.1

Re: [PATCH v6 1/1] arm64: Implement archrandom.h for ARMv8.5-RNG

[Mark Rutland]

On Wed, Nov 13, 2019 at 11:11:51AM +0100, richard.henderson@linaro.org wrote:
> From: Richard Henderson <richard.henderson@linaro.org>
> 
> Expose the ID_AA64ISAR0.RNDR field to userspace, as the
> RNG system registers are always available at EL0.

This patch does more than just that (e.g. implementing
arch_get_random_*()). Please write a more complete commit message.
That's where you should call out any gotchas.

[...]

> +/*
> + * The ALTERNATIVE infrastructure leads GCC to believe that the
> + * inline assembly is quite large, rather than two insns, which
> + * leads to the function being considered not profitable to inline.
> + * Override this decision with __always_inline.
> + */
> +static __always_inline __must_check
> +bool arch_get_random_seed_long(unsigned long *v)
> +{
> +	register unsigned long x0 __asm__("x0");
> +	unsigned long ok;
> +
> +	asm volatile(ALTERNATIVE_CB("bl boot_get_random_seed_long\n",
> +				    arm64_update_get_random_seed_long)
> +		     "cset %1, ne\n"
> +		     : "=r" (x0), "=r" (ok) : : "cc");
> +
> +	*v = x0;
> +	return ok;
> +}

> +/*
> + * Before alternatives are finalized, arch_get_random_seed_long calls
> + * this function.  The abi is as if
> + *
> + *     msr x0, rndr
> + *
> + * Preserve all other call-clobbered regs.
> + */
> +
> +asm(".globl	boot_get_random_seed_long\n"
> +".type	boot_get_random_seed_long, @function\n"
> +"boot_get_random_seed_long:\n"
> +"	stp	x29, x30, [sp, -160]!\n"
> +"	stp	x1, x2, [sp, 16]\n"
> +"	stp	x3, x4, [sp, 32]\n"
> +"	stp	x5, x6, [sp, 48]\n"
> +"	stp	x7, x8, [sp, 64]\n"
> +"	stp	x9, x10, [sp, 80]\n"
> +"	stp	x11, x12, [sp, 96]\n"
> +"	stp	x13, x14, [sp, 112]\n"
> +"	stp	x15, x16, [sp, 128]\n"
> +"	stp	x17, x18, [sp, 144]\n"
> +"	mov	x0, " __stringify(ARM64_HAS_RNG) "\n"
> +"	bl	this_cpu_has_cap\n"
> +"	ldp	x1, x2, [sp, 16]\n"
> +"	ldp	x3, x4, [sp, 32]\n"
> +"	ldp	x5, x6, [sp, 48]\n"
> +"	ldp	x7, x8, [sp, 64]\n"
> +"	ldp	x9, x10, [sp, 80]\n"
> +"	ldp	x11, x12, [sp, 96]\n"
> +"	ldp	x13, x14, [sp, 112]\n"
> +"	ldp	x15, x16, [sp, 128]\n"
> +"	ldp	x17, x18, [sp, 144]\n"
> +"	ldp	x29, x30, [sp], 160\n"
> +/* Test this_cpu_has_cap result, clearing x0 and setting Z if false. */
> +"	ands	w0, w0, #0xff\n"
> +"	beq	1f\n"
> +	__mrs_s("x0", SYS_RNDR_EL0) "\n"
> +"1:	ret\n"
> +".size boot_get_random_seed_long, . - boot_get_random_seed_long\n");
> +
> +
> +void arm64_update_get_random_seed_long(struct alt_instr *alt,
> +				       __le32 *origptr, __le32 *updptr,
> +				       int nr_inst)
> +{
> +	u32 insn;
> +
> +	BUG_ON(nr_inst != 1);
> +
> +	if (cpus_have_cap(ARM64_HAS_RNG))
> +		insn = 0xd53b2400;	/* mrs	x0, rndr */
> +	else
> +		insn = 0xea1f03e0;	/* ands	x0, xzr, xzr */
> +	updptr[0] = cpu_to_le32(insn);
> +}

Sorry if I wasn't sufficiently clear on this before, but I really want
this to be as braindead simple as possible, and so I don't think the
above is the right approach.

Rather than being clever, as above, please let's do this in a simpler
way. If we need to do something early on the boot CPU, we should either:

 * Have the common random init code (running on the boot CPU) use 
   specific early_arch_get_random_*() helpers; and have the arm64
   version of this check this_cpu_has_cap() to determine whether the
   boot CPU has the instruction.

 * Have the arm64 setup_arch() code call something that checks
   this_cpu_has_cap(), and have that explicitly feed entropy to the core
   code somehow.

The common case should just check the system cap, then use the
instruction. In either case the only patching should be for the cap.

Thanks,
Mark.