Unverified Commit 10243401 authored by Samuel Ortiz's avatar Samuel Ortiz Committed by Palmer Dabbelt
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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: default avatarConor Dooley <conor.dooley@microchip.com>
Signed-off-by: default avatarSamuel Ortiz <sameo@rivosinc.com>
Signed-off-by: default avatarClément Léger <cleger@rivosinc.com>
Link: https://lore.kernel.org/r/20231130111704.1319081-1-cleger@rivosinc.com


Signed-off-by: default avatarPalmer Dabbelt <palmer@rivosinc.com>
parent 55ca8d7a

arch/riscv/include/asm/archrandom.h

0 → 100644
+72 −0
Original line number Diff line number Diff line 
/* 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 */

arch/riscv/include/asm/csr.h

+9 −0
Original line number Diff line number Diff line
@@ -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