patch.c

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#include <linux/kernel.h>
#include <linux/kprobes.h>
#include <linux/stop_machine.h>

#include <asm/cacheflush.h>
#include <asm/smp_plat.h>
#include <asm/opcodes.h>

#include "patch.h"

struct patch {
    void *addr;
    unsigned int insn;
};

void __kprobes __patch_text(void *addr, unsigned int insn)
{
    bool thumb2 = IS_ENABLED(CONFIG_THUMB2_KERNEL);
    int size;

    if (thumb2 && __opcode_is_thumb16(insn)) {
        *(u16 *)addr = __opcode_to_mem_thumb16(insn);
        size = sizeof(u16);
    } else if (thumb2 && ((uintptr_t)addr & 2)) {
        u16 first = __opcode_thumb32_first(insn);
        u16 second = __opcode_thumb32_second(insn);
        u16 *addrh = addr;

        addrh[0] = __opcode_to_mem_thumb16(first);
        addrh[1] = __opcode_to_mem_thumb16(second);

        size = sizeof(u32);
    } else {
        if (thumb2)
            insn = __opcode_to_mem_thumb32(insn);
        else
            insn = __opcode_to_mem_arm(insn);

        *(u32 *)addr = insn;
        size = sizeof(u32);
    }

    flush_icache_range((uintptr_t)(addr),
               (uintptr_t)(addr) + size);
}

static int __kprobes patch_text_stop_machine(void *data)
{
    struct patch *patch = data;

    __patch_text(patch->addr, patch->insn);

    return 0;
}

void __kprobes patch_text(void *addr, unsigned int insn)
{
    struct patch patch = {
        .addr = addr,
        .insn = insn,
    };

    if (cache_ops_need_broadcast()) {
        stop_machine(patch_text_stop_machine, &patch, cpu_online_mask);
    } else {
        bool straddles_word = IS_ENABLED(CONFIG_THUMB2_KERNEL)
                      && __opcode_is_thumb32(insn)
                      && ((uintptr_t)addr & 2);

        if (straddles_word)
            stop_machine(patch_text_stop_machine, &patch, NULL);
        else
            __patch_text(addr, insn);
    }
}