// SPDX-License-Identifier: GPL-2.0
/*
 * This is for all the tests relating directly to Control Flow Integrity.
 */
#include "lkdtm.h"
#include <asm/page.h>

static int called_count;

/* Function taking one argument, without a return value. */
static noinline void lkdtm_increment_void(int *counter)
{
        (*counter)++;
}

/* Function taking one argument, returning int. */
static noinline int lkdtm_increment_int(int *counter)
{
        (*counter)++;

        return *counter;
}

/* Don't allow the compiler to inline the calls. */
static noinline void lkdtm_indirect_call(void (*func)(int *))
{
        func(&called_count);
}

/*
 * This tries to call an indirect function with a mismatched prototype.
 */
static void lkdtm_CFI_FORWARD_PROTO(void)
{
        /*
         * Matches lkdtm_increment_void()'s prototype, but not
         * lkdtm_increment_int()'s prototype.
         */
        pr_info("Calling matched prototype ...\n");
        lkdtm_indirect_call(lkdtm_increment_void);

        pr_info("Calling mismatched prototype ...\n");
        lkdtm_indirect_call((void *)lkdtm_increment_int);

        pr_err("FAIL: survived mismatched prototype function call!\n");
        pr_expected_config(CONFIG_CFI);
}

/*
 * This can stay local to LKDTM, as there should not be a production reason
 * to disable PAC && SCS.
 */
#ifdef CONFIG_ARM64_PTR_AUTH_KERNEL
# ifdef CONFIG_ARM64_BTI_KERNEL
#  define __no_pac             "branch-protection=bti"
# else
#  ifdef CONFIG_CC_HAS_BRANCH_PROT_PAC_RET
#   define __no_pac            "branch-protection=none"
#  else
#   define __no_pac            "sign-return-address=none"
#  endif
# endif
# define __no_ret_protection   __noscs __attribute__((__target__(__no_pac)))
#else
# define __no_ret_protection   __noscs
#endif

#define no_pac_addr(addr)      \
        ((__force __typeof__(addr))((uintptr_t)(addr) | PAGE_OFFSET))

#ifdef CONFIG_RISCV
/* https://github.com/riscv-non-isa/riscv-elf-psabi-doc/blob/master/riscv-cc.adoc#frame-pointer-convention */
#define FRAME_RA_OFFSET         (-1)
#else
#define FRAME_RA_OFFSET         1
#endif

/* The ultimate ROP gadget. */
static noinline __no_ret_protection
void set_return_addr_unchecked(unsigned long *expected, unsigned long *addr)
{
        /* Use of volatile is to make sure final write isn't seen as a dead store. */
        unsigned long * volatile *ret_addr =
                (unsigned long **)__builtin_frame_address(0) + FRAME_RA_OFFSET;

        /* Make sure we've found the right place on the stack before writing it. */
        if (no_pac_addr(*ret_addr) == expected)
                *ret_addr = (addr);
        else
                /* Check architecture, stack layout, or compiler behavior... */
                pr_warn("Eek: return address mismatch! %px != %px\n",
                        *ret_addr, addr);
}

static noinline
void set_return_addr(unsigned long *expected, unsigned long *addr)
{
        /* Use of volatile is to make sure final write isn't seen as a dead store. */
        unsigned long * volatile *ret_addr =
                (unsigned long **)__builtin_frame_address(0) + FRAME_RA_OFFSET;

        /* Make sure we've found the right place on the stack before writing it. */
        if (no_pac_addr(*ret_addr) == expected)
                *ret_addr = (addr);
        else
                /* Check architecture, stack layout, or compiler behavior... */
                pr_warn("Eek: return address mismatch! %px != %px\n",
                        *ret_addr, addr);
}

static volatile int force_check;

static void lkdtm_CFI_BACKWARD(void)
{
        /* Use calculated gotos to keep labels addressable. */
        void *labels[] = { NULL, &&normal, &&redirected, &&check_normal, &&check_redirected };

        pr_info("Attempting unchecked stack return address redirection ...\n");

        /* Always false */
        if (force_check) {
                /*
                 * Prepare to call with NULLs to avoid parameters being treated as
                 * constants in -02.
                 */
                set_return_addr_unchecked(NULL, NULL);
                set_return_addr(NULL, NULL);
                if (force_check)
                        goto *labels[1];
                if (force_check)
                        goto *labels[2];
                if (force_check)
                        goto *labels[3];
                if (force_check)
                        goto *labels[4];
                return;
        }

        /*
         * Use fallthrough switch case to keep basic block ordering between
         * set_return_addr*() and the label after it.
         */
        switch (force_check) {
        case 0:
                set_return_addr_unchecked(&&normal, &&redirected);
                fallthrough;
        case 1:
normal:
                /* Always true */
                if (!force_check) {
                        pr_err("FAIL: stack return address manipulation failed!\n");
                        /* If we can't redirect "normally", we can't test mitigations. */
                        return;
                }
                break;
        default:
redirected:
                pr_info("ok: redirected stack return address.\n");
                break;
        }

        pr_info("Attempting checked stack return address redirection ...\n");

        switch (force_check) {
        case 0:
                set_return_addr(&&check_normal, &&check_redirected);
                fallthrough;
        case 1:
check_normal:
                /* Always true */
                if (!force_check) {
                        pr_info("ok: control flow unchanged.\n");
                        return;
                }

check_redirected:
                pr_err("FAIL: stack return address was redirected!\n");
                break;
        }

        if (IS_ENABLED(CONFIG_ARM64_PTR_AUTH_KERNEL)) {
                pr_expected_config(CONFIG_ARM64_PTR_AUTH_KERNEL);
                return;
        }
        if (IS_ENABLED(CONFIG_SHADOW_CALL_STACK)) {
                pr_expected_config(CONFIG_SHADOW_CALL_STACK);
                return;
        }
        pr_warn("This is probably expected, since this %s was built *without* %s=y nor %s=y\n",
                lkdtm_kernel_info,
                "CONFIG_ARM64_PTR_AUTH_KERNEL", "CONFIG_SHADOW_CALL_STACK");
}

static struct crashtype crashtypes[] = {
        CRASHTYPE(CFI_FORWARD_PROTO),
        CRASHTYPE(CFI_BACKWARD),
};

struct crashtype_category cfi_crashtypes = {
        .crashtypes = crashtypes,
        .len        = ARRAY_SIZE(crashtypes),
};