diff options
author | Samuel Ortiz <sameo@rivosinc.com> | 2023-11-30 12:17:02 +0100 |
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committer | Palmer Dabbelt <palmer@rivosinc.com> | 2024-01-18 03:20:49 +0100 |
commit | 10243401059287868a5651f869a2494368872add (patch) | |
tree | a2a4b42d335b20de65d800407ee3f8188a4a5eff | |
parent | riscv: Optimize hweight API with Zbb extension (diff) | |
download | linux-10243401059287868a5651f869a2494368872add.tar.xz linux-10243401059287868a5651f869a2494368872add.zip |
RISC-V: Implement archrandom when Zkr is available
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 <conor.dooley@microchip.com>
Signed-off-by: Samuel Ortiz <sameo@rivosinc.com>
Signed-off-by: Clément Léger <cleger@rivosinc.com>
Link: https://lore.kernel.org/r/20231130111704.1319081-1-cleger@rivosinc.com
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>
-rw-r--r-- | arch/riscv/include/asm/archrandom.h | 72 | ||||
-rw-r--r-- | arch/riscv/include/asm/csr.h | 9 |
2 files changed, 81 insertions, 0 deletions
diff --git a/arch/riscv/include/asm/archrandom.h b/arch/riscv/include/asm/archrandom.h new file mode 100644 index 000000000000..5345360adfb9 --- /dev/null +++ b/arch/riscv/include/asm/archrandom.h @@ -0,0 +1,72 @@ +/* SPDX-License-Identifier: GPL-2.0 */ +/* + * Kernel interface for the RISCV arch_random_* functions + * + * Copyright (c) 2023 Rivos Inc. + * + */ + +#ifndef ASM_RISCV_ARCHRANDOM_H +#define ASM_RISCV_ARCHRANDOM_H + +#include <asm/csr.h> +#include <asm/processor.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); + unsigned long opst = csr_seed & SEED_OPST_MASK; + + switch (opst) { + 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: + cpu_relax(); + 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 |