path: root/target/arm/mte_helper.c

/*
 * ARM v8.5-MemTag Operations
 *
 * Copyright (c) 2020 Linaro, Ltd.
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, see <http://www.gnu.org/licenses/>.
 */

#include "qemu/osdep.h"
#include "cpu.h"
#include "internals.h"
#include "exec/exec-all.h"
#include "exec/cpu_ldst.h"
#include "exec/helper-proto.h"


static int choose_nonexcluded_tag(int tag, int offset, uint16_t exclude)
{
    if (exclude == 0xffff) {
        return 0;
    }
    if (offset == 0) {
        while (exclude & (1 << tag)) {
            tag = (tag + 1) & 15;
        }
    } else {
        do {
            do {
                tag = (tag + 1) & 15;
            } while (exclude & (1 << tag));
        } while (--offset > 0);
    }
    return tag;
}

/**
 * allocation_tag_mem:
 * @env: the cpu environment
 * @ptr_mmu_idx: the addressing regime to use for the virtual address
 * @ptr: the virtual address for which to look up tag memory
 * @ptr_access: the access to use for the virtual address
 * @ptr_size: the number of bytes in the normal memory access
 * @tag_access: the access to use for the tag memory
 * @tag_size: the number of bytes in the tag memory access
 * @ra: the return address for exception handling
 *
 * Our tag memory is formatted as a sequence of little-endian nibbles.
 * That is, the byte at (addr >> (LOG2_TAG_GRANULE + 1)) contains two
 * tags, with the tag at [3:0] for the lower addr and the tag at [7:4]
 * for the higher addr.
 *
 * Here, resolve the physical address from the virtual address, and return
 * a pointer to the corresponding tag byte.  Exit with exception if the
 * virtual address is not accessible for @ptr_access.
 *
 * The @ptr_size and @tag_size values may not have an obvious relation
 * due to the alignment of @ptr, and the number of tag checks required.
 *
 * If there is no tag storage corresponding to @ptr, return NULL.
 */
static uint8_t *allocation_tag_mem(CPUARMState *env, int ptr_mmu_idx,
                                   uint64_t ptr, MMUAccessType ptr_access,
                                   int ptr_size, MMUAccessType tag_access,
                                   int tag_size, uintptr_t ra)
{
    /* Tag storage not implemented.  */
    return NULL;
}

uint64_t HELPER(irg)(CPUARMState *env, uint64_t rn, uint64_t rm)
{
    int rtag;

    /*
     * Our IMPDEF choice for GCR_EL1.RRND==1 is to behave as if
     * GCR_EL1.RRND==0, always producing deterministic results.
     */
    uint16_t exclude = extract32(rm | env->cp15.gcr_el1, 0, 16);
    int start = extract32(env->cp15.rgsr_el1, 0, 4);
    int seed = extract32(env->cp15.rgsr_el1, 8, 16);
    int offset, i;

    /* RandomTag */
    for (i = offset = 0; i < 4; ++i) {
        /* NextRandomTagBit */
        int top = (extract32(seed, 5, 1) ^ extract32(seed, 3, 1) ^
                   extract32(seed, 2, 1) ^ extract32(seed, 0, 1));
        seed = (top << 15) | (seed >> 1);
        offset |= top << i;
    }
    rtag = choose_nonexcluded_tag(start, offset, exclude);
    env->cp15.rgsr_el1 = rtag | (seed << 8);

    return address_with_allocation_tag(rn, rtag);
}

uint64_t HELPER(addsubg)(CPUARMState *env, uint64_t ptr,
                         int32_t offset, uint32_t tag_offset)
{
    int start_tag = allocation_tag_from_addr(ptr);
    uint16_t exclude = extract32(env->cp15.gcr_el1, 0, 16);
    int rtag = choose_nonexcluded_tag(start_tag, tag_offset, exclude);

    return address_with_allocation_tag(ptr + offset, rtag);
}

static int load_tag1(uint64_t ptr, uint8_t *mem)
{
    int ofs = extract32(ptr, LOG2_TAG_GRANULE, 1) * 4;
    return extract32(*mem, ofs, 4);
}

uint64_t HELPER(ldg)(CPUARMState *env, uint64_t ptr, uint64_t xt)
{
    int mmu_idx = cpu_mmu_index(env, false);
    uint8_t *mem;
    int rtag = 0;

    /* Trap if accessing an invalid page.  */
    mem = allocation_tag_mem(env, mmu_idx, ptr, MMU_DATA_LOAD, 1,
                             MMU_DATA_LOAD, 1, GETPC());

    /* Load if page supports tags. */
    if (mem) {
        rtag = load_tag1(ptr, mem);
    }

    return address_with_allocation_tag(xt, rtag);
}

static void check_tag_aligned(CPUARMState *env, uint64_t ptr, uintptr_t ra)
{
    if (unlikely(!QEMU_IS_ALIGNED(ptr, TAG_GRANULE))) {
        arm_cpu_do_unaligned_access(env_cpu(env), ptr, MMU_DATA_STORE,
                                    cpu_mmu_index(env, false), ra);
        g_assert_not_reached();
    }
}

/* For use in a non-parallel context, store to the given nibble.  */
static void store_tag1(uint64_t ptr, uint8_t *mem, int tag)
{
    int ofs = extract32(ptr, LOG2_TAG_GRANULE, 1) * 4;
    *mem = deposit32(*mem, ofs, 4, tag);
}

/* For use in a parallel context, atomically store to the given nibble.  */
static void store_tag1_parallel(uint64_t ptr, uint8_t *mem, int tag)
{
    int ofs = extract32(ptr, LOG2_TAG_GRANULE, 1) * 4;
    uint8_t old = atomic_read(mem);

    while (1) {
        uint8_t new = deposit32(old, ofs, 4, tag);
        uint8_t cmp = atomic_cmpxchg(mem, old, new);
        if (likely(cmp == old)) {
            return;
        }
        old = cmp;
    }
}

typedef void stg_store1(uint64_t, uint8_t *, int);

static inline void do_stg(CPUARMState *env, uint64_t ptr, uint64_t xt,
                          uintptr_t ra, stg_store1 store1)
{
    int mmu_idx = cpu_mmu_index(env, false);
    uint8_t *mem;

    check_tag_aligned(env, ptr, ra);

    /* Trap if accessing an invalid page.  */
    mem = allocation_tag_mem(env, mmu_idx, ptr, MMU_DATA_STORE, TAG_GRANULE,
                             MMU_DATA_STORE, 1, ra);

    /* Store if page supports tags. */
    if (mem) {
        store1(ptr, mem, allocation_tag_from_addr(xt));
    }
}

void HELPER(stg)(CPUARMState *env, uint64_t ptr, uint64_t xt)
{
    do_stg(env, ptr, xt, GETPC(), store_tag1);
}

void HELPER(stg_parallel)(CPUARMState *env, uint64_t ptr, uint64_t xt)
{
    do_stg(env, ptr, xt, GETPC(), store_tag1_parallel);
}

void HELPER(stg_stub)(CPUARMState *env, uint64_t ptr)
{
    int mmu_idx = cpu_mmu_index(env, false);
    uintptr_t ra = GETPC();

    check_tag_aligned(env, ptr, ra);
    probe_write(env, ptr, TAG_GRANULE, mmu_idx, ra);
}

static inline void do_st2g(CPUARMState *env, uint64_t ptr, uint64_t xt,
                           uintptr_t ra, stg_store1 store1)
{
    int mmu_idx = cpu_mmu_index(env, false);
    int tag = allocation_tag_from_addr(xt);
    uint8_t *mem1, *mem2;

    check_tag_aligned(env, ptr, ra);

    /*
     * Trap if accessing an invalid page(s).
     * This takes priority over !allocation_tag_access_enabled.
     */
    if (ptr & TAG_GRANULE) {
        /* Two stores unaligned mod TAG_GRANULE*2 -- modify two bytes. */
        mem1 = allocation_tag_mem(env, mmu_idx, ptr, MMU_DATA_STORE,
                                  TAG_GRANULE, MMU_DATA_STORE, 1, ra);
        mem2 = allocation_tag_mem(env, mmu_idx, ptr + TAG_GRANULE,
                                  MMU_DATA_STORE, TAG_GRANULE,
                                  MMU_DATA_STORE, 1, ra);

        /* Store if page(s) support tags. */
        if (mem1) {
            store1(TAG_GRANULE, mem1, tag);
        }
        if (mem2) {
            store1(0, mem2, tag);
        }
    } else {
        /* Two stores aligned mod TAG_GRANULE*2 -- modify one byte. */
        mem1 = allocation_tag_mem(env, mmu_idx, ptr, MMU_DATA_STORE,
                                  2 * TAG_GRANULE, MMU_DATA_STORE, 1, ra);
        if (mem1) {
            tag |= tag << 4;
            atomic_set(mem1, tag);
        }
    }
}

void HELPER(st2g)(CPUARMState *env, uint64_t ptr, uint64_t xt)
{
    do_st2g(env, ptr, xt, GETPC(), store_tag1);
}

void HELPER(st2g_parallel)(CPUARMState *env, uint64_t ptr, uint64_t xt)
{
    do_st2g(env, ptr, xt, GETPC(), store_tag1_parallel);
}

void HELPER(st2g_stub)(CPUARMState *env, uint64_t ptr)
{
    int mmu_idx = cpu_mmu_index(env, false);
    uintptr_t ra = GETPC();
    int in_page = -(ptr | TARGET_PAGE_MASK);

    check_tag_aligned(env, ptr, ra);

    if (likely(in_page >= 2 * TAG_GRANULE)) {
        probe_write(env, ptr, 2 * TAG_GRANULE, mmu_idx, ra);
    } else {
        probe_write(env, ptr, TAG_GRANULE, mmu_idx, ra);
        probe_write(env, ptr + TAG_GRANULE, TAG_GRANULE, mmu_idx, ra);
    }
}