/*      $OpenBSD: codepatch.c,v 1.1 2026/06/23 11:45:54 kettenis Exp $  */
/*
 * Copyright (c) 2014-2015 Stefan Fritsch <sf@sfritsch.de>
 *
 * Permission to use, copy, modify, and distribute this software for any
 * purpose with or without fee is hereby granted, provided that the above
 * copyright notice and this permission notice appear in all copies.
 *
 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 */

#include <sys/param.h>
#include <sys/systm.h>
#include <machine/codepatch.h>
#include <machine/cpufunc.h>
#include <uvm/uvm_extern.h> /* round_page */

#ifdef CODEPATCH_DEBUG
#define DBGPRINT(fmt, args...)  printf("%s: " fmt "\n", __func__, ## args)
#else
#define DBGPRINT(fmt, args...)  do {} while (0)
#endif

struct codepatch {
        vaddr_t addr;
        uint16_t len;
        uint16_t tag;
        uint32_t _padding;
};
CTASSERT(sizeof(struct codepatch) % 8 == 0);

extern struct codepatch codepatch_begin;
extern struct codepatch codepatch_end;
extern char __cptext_start[];
extern char __cptext_end[];

void
codepatch_fill_nop(void *caddr, uint16_t len)
{
        uint32_t *addr = caddr;

        while (len > 3) {
                *addr++ = 0xd503201f;
                len -= 4;
        }
        cpu_icache_sync_range((vaddr_t)caddr, len);
}

/*
 * Create writeable aliases of memory we need
 * to write to as kernel is mapped read-only
 */
void *
codepatch_maprw(vaddr_t *nva, vaddr_t dest)
{
        paddr_t kva = trunc_page((paddr_t)dest);
        paddr_t po = (paddr_t)dest & PAGE_MASK;
        paddr_t pa1, pa2;

        if (*nva == 0)
                *nva = (vaddr_t)km_alloc(2 * PAGE_SIZE, &kv_any, &kp_none,
                                        &kd_waitok);

        pmap_extract(pmap_kernel(), kva, &pa1);
        pmap_extract(pmap_kernel(), kva + PAGE_SIZE, &pa2);
        pmap_kenter_pa(*nva, pa1, PROT_READ | PROT_WRITE);
        pmap_kenter_pa(*nva + PAGE_SIZE, pa2, PROT_READ | PROT_WRITE);
        pmap_update(pmap_kernel());

        return (void *)(*nva + po);
}

void
codepatch_unmaprw(vaddr_t nva)
{
        if (nva == 0)
                return;
        pmap_kremove(nva, 2 * PAGE_SIZE);
        km_free((void *)nva, 2 * PAGE_SIZE, &kv_any, &kp_none);
}

/* Patch with NOPs */
void
codepatch_nop(uint16_t tag)
{
        struct codepatch *patch;
        unsigned char *rwaddr;
        vaddr_t rwmap = 0;
        int i = 0;

        DBGPRINT("patching tag %u", tag);

        for (patch = &codepatch_begin; patch < &codepatch_end; patch++) {
                if (patch->tag != tag)
                        continue;
                rwaddr = codepatch_maprw(&rwmap, patch->addr);
                codepatch_fill_nop(rwaddr, patch->len);
                i++;
        }
        codepatch_unmaprw(rwmap);
        DBGPRINT("patched %d places", i);
}

void
codepatch_disable(void)
{
        size_t size = round_page(__cptext_end - __cptext_start);
        /* If this assert fails, something is wrong with the cptext section */
        KASSERT(size > 0);
        pmap_kremove((vaddr_t)__cptext_start, size);
        pmap_update(pmap_kernel());
        DBGPRINT("%s: Unmapped %#zx bytes\n", __func__, size);
}