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VDSO time functions do not call any other function, so they don't need to save/restore LR. However, retrieving the address of VDSO data page requires using LR hence saving then restoring it, which can be heavy on some CPUs. On the other hand, VDSO functions on powerpc are not standard functions and require a wrapper function to call C VDSO functions. And that wrapper has to save and restore LR in order to call the C VDSO function, so retrieving VDSO data page address in that wrapper doesn't require additional save/restore of LR. For random VDSO functions it is a bit different. Because the function calls __arch_chacha20_blocks_nostack(), it saves and restores LR. Retrieving VDSO data page address can then be done there without additional save/restore of LR. So lets implement __arch_get_vdso_rng_data() and simplify the wrapper. It starts paving the way for the day powerpc will implement a more standard ABI for VDSO functions. Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> Link: https://patch.msgid.link/a1a9bd0df508f1b5c04684b7366940577dfc6262.1727858295.git.christophe.leroy@csgroup.eu
67 lines
1.8 KiB
C
67 lines
1.8 KiB
C
/* SPDX-License-Identifier: GPL-2.0 */
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/*
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* Copyright (C) 2024 Christophe Leroy <christophe.leroy@csgroup.eu>, CS GROUP France
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*/
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#ifndef _ASM_POWERPC_VDSO_GETRANDOM_H
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#define _ASM_POWERPC_VDSO_GETRANDOM_H
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#ifndef __ASSEMBLY__
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#include <asm/vdso_datapage.h>
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static __always_inline int do_syscall_3(const unsigned long _r0, const unsigned long _r3,
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const unsigned long _r4, const unsigned long _r5)
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{
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register long r0 asm("r0") = _r0;
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register unsigned long r3 asm("r3") = _r3;
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register unsigned long r4 asm("r4") = _r4;
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register unsigned long r5 asm("r5") = _r5;
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register int ret asm ("r3");
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asm volatile(
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" sc\n"
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" bns+ 1f\n"
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" neg %0, %0\n"
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"1:\n"
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: "=r" (ret), "+r" (r4), "+r" (r5), "+r" (r0)
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: "r" (r3)
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: "memory", "r6", "r7", "r8", "r9", "r10", "r11", "r12", "cr0", "ctr");
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return ret;
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}
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/**
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* getrandom_syscall - Invoke the getrandom() syscall.
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* @buffer: Destination buffer to fill with random bytes.
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* @len: Size of @buffer in bytes.
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* @flags: Zero or more GRND_* flags.
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* Returns: The number of bytes written to @buffer, or a negative value indicating an error.
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*/
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static __always_inline ssize_t getrandom_syscall(void *buffer, size_t len, unsigned int flags)
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{
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return do_syscall_3(__NR_getrandom, (unsigned long)buffer,
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(unsigned long)len, (unsigned long)flags);
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}
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static __always_inline struct vdso_rng_data *__arch_get_vdso_rng_data(void)
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{
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struct vdso_arch_data *data;
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asm (
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" bcl 20, 31, .+4 ;"
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"0: mflr %0 ;"
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" addis %0, %0, (_vdso_datapage - 0b)@ha ;"
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" addi %0, %0, (_vdso_datapage - 0b)@l ;"
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: "=r" (data) : : "lr"
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);
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return &data->rng_data;
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}
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ssize_t __c_kernel_getrandom(void *buffer, size_t len, unsigned int flags, void *opaque_state,
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size_t opaque_len);
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#endif /* !__ASSEMBLY__ */
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#endif /* _ASM_POWERPC_VDSO_GETRANDOM_H */
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