poly1305.h

/* SPDX-License-Identifier: GPL-2.0 OR MIT */
/*
 * Copyright (C) 2015-2019 Jason A. Donenfeld <[email protected]>. All Rights Reserved.
 */

#include <asm/cpu_device_id.h>
#include <asm/fpu/api.h>
#include <linux/jump_label.h>
#include <linux/kernel.h>
#include <linux/sizes.h>

struct poly1305_arch_internal {
	union {
		struct {
			u32 h[5];
			u32 is_base2_26;
		};
		u64 hs[3];
	};
	u64 r[2];
	u64 pad;
	struct { u32 r2, r1, r4, r3; } rn[9];
};

/*
 * The AVX code uses base 2^26, while the scalar code uses base 2^64. If we hit
 * the unfortunate situation of using AVX and then having to go back to scalar
 * -- because the user is silly and has called the update function from two
 * separate contexts -- then we need to convert back to the original base before
 * proceeding. It is possible to reason that the initial reduction below is
 * sufficient given the implementation invariants. However, for an avoidance of
 * doubt and because this is not performance critical, we do the full reduction
 * anyway. Z3 proof of below function: https://xn--4db.cc/ltPtHCKN/py
 */
static void convert_to_base2_64(void *ctx)
{
	struct poly1305_arch_internal *state = ctx;
	u32 cy;

	if (!state->is_base2_26)
		return;

	cy = state->h[0] >> 26; state->h[0] &= 0x3ffffff; state->h[1] += cy;
	cy = state->h[1] >> 26; state->h[1] &= 0x3ffffff; state->h[2] += cy;
	cy = state->h[2] >> 26; state->h[2] &= 0x3ffffff; state->h[3] += cy;
	cy = state->h[3] >> 26; state->h[3] &= 0x3ffffff; state->h[4] += cy;
	state->hs[0] = ((u64)state->h[2] << 52) | ((u64)state->h[1] << 26) | state->h[0];
	state->hs[1] = ((u64)state->h[4] << 40) | ((u64)state->h[3] << 14) | (state->h[2] >> 12);
	state->hs[2] = state->h[4] >> 24;
	/* Unsigned Less Than: branchlessly produces 1 if a < b, else 0. */
#define ULT(a, b) ((a ^ ((a ^ b) | ((a - b) ^ b))) >> (sizeof(a) * 8 - 1))
	cy = (state->hs[2] >> 2) + (state->hs[2] & ~3ULL);
	state->hs[2] &= 3;
	state->hs[0] += cy;
	state->hs[1] += (cy = ULT(state->hs[0], cy));
	state->hs[2] += ULT(state->hs[1], cy);
#undef ULT
	state->is_base2_26 = 0;
}

asmlinkage void poly1305_init_x86_64(struct poly1305_block_state *state,
				     const u8 raw_key[POLY1305_BLOCK_SIZE]);
asmlinkage void poly1305_blocks_x86_64(struct poly1305_arch_internal *ctx,
				       const u8 *inp,
				       const size_t len, const u32 padbit);
asmlinkage void poly1305_emit_x86_64(const struct poly1305_state *ctx,
				     u8 mac[POLY1305_DIGEST_SIZE],
				     const u32 nonce[4]);
asmlinkage void poly1305_emit_avx(const struct poly1305_state *ctx,
				  u8 mac[POLY1305_DIGEST_SIZE],
				  const u32 nonce[4]);
asmlinkage void poly1305_blocks_avx(struct poly1305_arch_internal *ctx,
				    const u8 *inp, const size_t len,
				    const u32 padbit);
asmlinkage void poly1305_blocks_avx2(struct poly1305_arch_internal *ctx,
				     const u8 *inp, const size_t len,
				     const u32 padbit);
asmlinkage void poly1305_blocks_avx512(struct poly1305_arch_internal *ctx,
				       const u8 *inp,
				       const size_t len, const u32 padbit);

static __ro_after_init DEFINE_STATIC_KEY_FALSE(poly1305_use_avx);
static __ro_after_init DEFINE_STATIC_KEY_FALSE(poly1305_use_avx2);
static __ro_after_init DEFINE_STATIC_KEY_FALSE(poly1305_use_avx512);

static void poly1305_block_init(struct poly1305_block_state *state,
				const u8 raw_key[POLY1305_BLOCK_SIZE])
{
	poly1305_init_x86_64(state, raw_key);
}

static void poly1305_blocks(struct poly1305_block_state *state, const u8 *inp,
			    unsigned int len, u32 padbit)
{
	struct poly1305_arch_internal *ctx =
		container_of(&state->h.h, struct poly1305_arch_internal, h);

	/* SIMD disables preemption, so relax after processing each page. */
	BUILD_BUG_ON(SZ_4K < POLY1305_BLOCK_SIZE ||
		     SZ_4K % POLY1305_BLOCK_SIZE);

	/*
	 * The AVX implementations have significant setup overhead (e.g. key
	 * power computation, kernel FPU enabling) which makes them slower for
	 * short messages.  Fall back to the scalar implementation for messages
	 * shorter than 288 bytes, unless the AVX-specific key setup has already
	 * been performed (indicated by ctx->is_base2_26).
	 */
	if (!static_branch_likely(&poly1305_use_avx) ||
	    (len < POLY1305_BLOCK_SIZE * 18 && !ctx->is_base2_26) ||
	    unlikely(!irq_fpu_usable())) {
		convert_to_base2_64(ctx);
		poly1305_blocks_x86_64(ctx, inp, len, padbit);
		return;
	}

	do {
		const unsigned int bytes = min(len, SZ_4K);

		kernel_fpu_begin();
		if (static_branch_likely(&poly1305_use_avx512))
			poly1305_blocks_avx512(ctx, inp, bytes, padbit);
		else if (static_branch_likely(&poly1305_use_avx2))
			poly1305_blocks_avx2(ctx, inp, bytes, padbit);
		else
			poly1305_blocks_avx(ctx, inp, bytes, padbit);
		kernel_fpu_end();

		len -= bytes;
		inp += bytes;
	} while (len);
}

static void poly1305_emit(const struct poly1305_state *ctx,
			  u8 mac[POLY1305_DIGEST_SIZE], const u32 nonce[4])
{
	if (!static_branch_likely(&poly1305_use_avx))
		poly1305_emit_x86_64(ctx, mac, nonce);
	else
		poly1305_emit_avx(ctx, mac, nonce);
}

#define poly1305_mod_init_arch poly1305_mod_init_arch
static void poly1305_mod_init_arch(void)
{
	if (boot_cpu_has(X86_FEATURE_AVX) &&
	    cpu_has_xfeatures(XFEATURE_MASK_SSE | XFEATURE_MASK_YMM, NULL))
		static_branch_enable(&poly1305_use_avx);
	if (boot_cpu_has(X86_FEATURE_AVX) && boot_cpu_has(X86_FEATURE_AVX2) &&
	    cpu_has_xfeatures(XFEATURE_MASK_SSE | XFEATURE_MASK_YMM, NULL))
		static_branch_enable(&poly1305_use_avx2);
	if (boot_cpu_has(X86_FEATURE_AVX) && boot_cpu_has(X86_FEATURE_AVX2) &&
	    boot_cpu_has(X86_FEATURE_AVX512F) &&
	    cpu_has_xfeatures(XFEATURE_MASK_SSE | XFEATURE_MASK_YMM | XFEATURE_MASK_AVX512, NULL) &&
	    /* Skylake downclocks unacceptably much when using zmm, but later generations are fast. */
	    boot_cpu_data.x86_vfm != INTEL_SKYLAKE_X)
		static_branch_enable(&poly1305_use_avx512);
}