From: Samuel Ortiz <[email protected]>
From: Samuel Ortiz <[email protected]>
The Zkr extension is ratified and provides 16 bits of entropy seed when
reading the SEED CSR.
We can implement arch_get_random_seed_longs() by doing multiple csrrw to
that CSR and filling an unsigned long with valid entropy bits.
Acked-by: Conor Dooley <[email protected]>
Signed-off-by: Samuel Ortiz <[email protected]>
Signed-off-by: Clément Léger <[email protected]>
---
This series depends on "riscv: report more ISA extensions through
hwprobe" series [1].
Link: https://lore.kernel.org/lkml/[email protected]/ [1]
---
arch/riscv/include/asm/archrandom.h | 69 +++++++++++++++++++++++++++++
arch/riscv/include/asm/csr.h | 9 ++++
2 files changed, 78 insertions(+)
create mode 100644 arch/riscv/include/asm/archrandom.h
diff --git a/arch/riscv/include/asm/archrandom.h b/arch/riscv/include/asm/archrandom.h
new file mode 100644
index 000000000000..795837ccb583
--- /dev/null
+++ b/arch/riscv/include/asm/archrandom.h
@@ -0,0 +1,69 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Kernel interface for the RISCV arch_random_* functions
+ *
+ * Copyright (c) 2023 by Rivos Inc.
+ *
+ */
+
+#ifndef ASM_RISCV_ARCHRANDOM_H
+#define ASM_RISCV_ARCHRANDOM_H
+
+#include <asm/csr.h>
+
+#define SEED_RETRY_LOOPS 100
+
+static inline bool __must_check csr_seed_long(unsigned long *v)
+{
+ unsigned int retry = SEED_RETRY_LOOPS, valid_seeds = 0;
+ const int needed_seeds = sizeof(long) / sizeof(u16);
+ u16 *entropy = (u16 *)v;
+
+ do {
+ /*
+ * The SEED CSR must be accessed with a read-write instruction.
+ */
+ unsigned long csr_seed = csr_swap(CSR_SEED, 0);
+
+ switch (csr_seed & SEED_OPST_MASK) {
+ case SEED_OPST_ES16:
+ entropy[valid_seeds++] = csr_seed & SEED_ENTROPY_MASK;
+ if (valid_seeds == needed_seeds)
+ return true;
+ break;
+
+ case SEED_OPST_DEAD:
+ pr_err_once("archrandom: Unrecoverable error\n");
+ return false;
+
+ case SEED_OPST_BIST:
+ case SEED_OPST_WAIT:
+ default:
+ continue;
+ }
+ } while (--retry);
+
+ return false;
+}
+
+static inline size_t __must_check arch_get_random_longs(unsigned long *v, size_t max_longs)
+{
+ return 0;
+}
+
+static inline size_t __must_check arch_get_random_seed_longs(unsigned long *v, size_t max_longs)
+{
+ if (!max_longs)
+ return 0;
+
+ /*
+ * If Zkr is supported and csr_seed_long succeeds, we return one long
+ * worth of entropy.
+ */
+ if (riscv_has_extension_likely(RISCV_ISA_EXT_ZKR) && csr_seed_long(v))
+ return 1;
+
+ return 0;
+}
+
+#endif /* ASM_RISCV_ARCHRANDOM_H */
diff --git a/arch/riscv/include/asm/csr.h b/arch/riscv/include/asm/csr.h
index 306a19a5509c..510014051f5d 100644
--- a/arch/riscv/include/asm/csr.h
+++ b/arch/riscv/include/asm/csr.h
@@ -411,6 +411,15 @@
#define CSR_VTYPE 0xc21
#define CSR_VLENB 0xc22
+/* Scalar Crypto Extension - Entropy */
+#define CSR_SEED 0x015
+#define SEED_OPST_MASK _AC(0xC0000000, UL)
+#define SEED_OPST_BIST _AC(0x00000000, UL)
+#define SEED_OPST_WAIT _AC(0x40000000, UL)
+#define SEED_OPST_ES16 _AC(0x80000000, UL)
+#define SEED_OPST_DEAD _AC(0xC0000000, UL)
+#define SEED_ENTROPY_MASK _AC(0xFFFF, UL)
+
#ifdef CONFIG_RISCV_M_MODE
# define CSR_STATUS CSR_MSTATUS
# define CSR_IE CSR_MIE
--
2.42.0
On 29/11/2023 17:15, Ben Dooks wrote:
> On 29/11/2023 16:03, Clément Léger wrote:
>> From: Samuel Ortiz <[email protected]>
>>
>> From: Samuel Ortiz <[email protected]>
>>
>> The Zkr extension is ratified and provides 16 bits of entropy seed when
>> reading the SEED CSR.
>>
>> We can implement arch_get_random_seed_longs() by doing multiple csrrw to
>> that CSR and filling an unsigned long with valid entropy bits.
>>
>> Acked-by: Conor Dooley <[email protected]>
>> Signed-off-by: Samuel Ortiz <[email protected]>
>> Signed-off-by: Clément Léger <[email protected]>
>>
>> ---
>>
>> This series depends on "riscv: report more ISA extensions through
>> hwprobe" series [1].
>>
>> Link:
>> https://lore.kernel.org/lkml/[email protected]/ [1]
>> ---
>> arch/riscv/include/asm/archrandom.h | 69 +++++++++++++++++++++++++++++
>> arch/riscv/include/asm/csr.h | 9 ++++
>> 2 files changed, 78 insertions(+)
>> create mode 100644 arch/riscv/include/asm/archrandom.h
>>
>> diff --git a/arch/riscv/include/asm/archrandom.h
>> b/arch/riscv/include/asm/archrandom.h
>> new file mode 100644
>> index 000000000000..795837ccb583
>> --- /dev/null
>> +++ b/arch/riscv/include/asm/archrandom.h
>> @@ -0,0 +1,69 @@
>> +/* SPDX-License-Identifier: GPL-2.0 */
>> +/*
>> + * Kernel interface for the RISCV arch_random_* functions
>> + *
>> + * Copyright (c) 2023 by Rivos Inc.
>> + *
>> + */
>> +
>> +#ifndef ASM_RISCV_ARCHRANDOM_H
>> +#define ASM_RISCV_ARCHRANDOM_H
>> +
>> +#include <asm/csr.h>
>> +
>> +#define SEED_RETRY_LOOPS 100
>> +
>> +static inline bool __must_check csr_seed_long(unsigned long *v)
>> +{
>> + unsigned int retry = SEED_RETRY_LOOPS, valid_seeds = 0;
>> + const int needed_seeds = sizeof(long) / sizeof(u16);
>> + u16 *entropy = (u16 *)v;
>> +
>> + do {
>> + /*
>> + * The SEED CSR must be accessed with a read-write instruction.
>> + */
>> + unsigned long csr_seed = csr_swap(CSR_SEED, 0);
>> +
>> + switch (csr_seed & SEED_OPST_MASK) {
>> + case SEED_OPST_ES16:
>> + entropy[valid_seeds++] = csr_seed & SEED_ENTROPY_MASK;
>> + if (valid_seeds == needed_seeds)
>> + return true;
>> + break;
>> +
>> + case SEED_OPST_DEAD:
>> + pr_err_once("archrandom: Unrecoverable error\n");
>> + return false;
>> +
>> + case SEED_OPST_BIST:
>> + case SEED_OPST_WAIT:
>> + default:
>> + continue;
>
> is it worth adding a cpu_relax() here?
Yeah, that clearly makes sense !
>
>> + }
>> + } while (--retry);
>> +
>> + return false;
>> +}
>> +
>> +static inline size_t __must_check arch_get_random_longs(unsigned long
>> *v, size_t max_longs)
>> +{
>> + return 0;
>> +}
>> +
>> +static inline size_t __must_check arch_get_random_seed_longs(unsigned
>> long *v, size_t max_longs)
>> +{
>> + if (!max_longs)
>> + return 0;
>> +
>> + /*
>> + * If Zkr is supported and csr_seed_long succeeds, we return one
>> long
>> + * worth of entropy.
>> + */
>> + if (riscv_has_extension_likely(RISCV_ISA_EXT_ZKR) &&
>> csr_seed_long(v))
>> + return 1;
>
> I'm assuming the code will retry if max_longs > 1 ?
Yes the caller will call it until gathering enough data (see
drivers/char/random.c).
Thanks,
Clément
>
>
>
>> + return 0;
>> +}
>> +
>> +#endif /* ASM_RISCV_ARCHRANDOM_H */
>> diff --git a/arch/riscv/include/asm/csr.h b/arch/riscv/include/asm/csr.h
>> index 306a19a5509c..510014051f5d 100644
>> --- a/arch/riscv/include/asm/csr.h
>> +++ b/arch/riscv/include/asm/csr.h
>> @@ -411,6 +411,15 @@
>> #define CSR_VTYPE 0xc21
>> #define CSR_VLENB 0xc22
>> +/* Scalar Crypto Extension - Entropy */
>> +#define CSR_SEED 0x015
>> +#define SEED_OPST_MASK _AC(0xC0000000, UL)
>> +#define SEED_OPST_BIST _AC(0x00000000, UL)
>> +#define SEED_OPST_WAIT _AC(0x40000000, UL)
>> +#define SEED_OPST_ES16 _AC(0x80000000, UL)
>> +#define SEED_OPST_DEAD _AC(0xC0000000, UL)
>> +#define SEED_ENTROPY_MASK _AC(0xFFFF, UL)
>> +
>> #ifdef CONFIG_RISCV_M_MODE
>> # define CSR_STATUS CSR_MSTATUS
>> # define CSR_IE CSR_MIE
>