path: root/arch/powerpc/lib/code-patching.c

// SPDX-License-Identifier: GPL-2.0-or-later
/*
 *  Copyright 2008 Michael Ellerman, IBM Corporation.
 */

#include <linux/kernel.h>
#include <linux/kprobes.h>
#include <linux/vmalloc.h>
#include <linux/init.h>
#include <linux/mm.h>
#include <linux/cpuhotplug.h>
#include <linux/slab.h>
#include <linux/uaccess.h>

#include <asm/tlbflush.h>
#include <asm/page.h>
#include <asm/code-patching.h>
#include <asm/inst.h>

static int __patch_instruction(u32 *exec_addr, ppc_inst_t instr, u32 *patch_addr)
{
	if (!ppc_inst_prefixed(instr)) {
		u32 val = ppc_inst_val(instr);

		__put_kernel_nofault(patch_addr, &val, u32, failed);
	} else {
		u64 val = ppc_inst_as_ulong(instr);

		__put_kernel_nofault(patch_addr, &val, u64, failed);
	}

	asm ("dcbst 0, %0; sync; icbi 0,%1; sync; isync" :: "r" (patch_addr),
							    "r" (exec_addr));

	return 0;

failed:
	return -EFAULT;
}

int raw_patch_instruction(u32 *addr, ppc_inst_t instr)
{
	return __patch_instruction(addr, instr, addr);
}

#ifdef CONFIG_STRICT_KERNEL_RWX
static DEFINE_PER_CPU(struct vm_struct *, text_poke_area);

static int text_area_cpu_up(unsigned int cpu)
{
	struct vm_struct *area;

	area = get_vm_area(PAGE_SIZE, VM_ALLOC);
	if (!area) {
		WARN_ONCE(1, "Failed to create text area for cpu %d\n",
			cpu);
		return -1;
	}
	this_cpu_write(text_poke_area, area);

	return 0;
}

static int text_area_cpu_down(unsigned int cpu)
{
	free_vm_area(this_cpu_read(text_poke_area));
	return 0;
}

/*
 * Although BUG_ON() is rude, in this case it should only happen if ENOMEM, and
 * we judge it as being preferable to a kernel that will crash later when
 * someone tries to use patch_instruction().
 */
void __init poking_init(void)
{
	BUG_ON(!cpuhp_setup_state(CPUHP_AP_ONLINE_DYN,
		"powerpc/text_poke:online", text_area_cpu_up,
		text_area_cpu_down));
}

/*
 * This can be called for kernel text or a module.
 */
static int map_patch_area(void *addr, unsigned long text_poke_addr)
{
	unsigned long pfn;

	if (is_vmalloc_or_module_addr(addr))
		pfn = vmalloc_to_pfn(addr);
	else
		pfn = __pa_symbol(addr) >> PAGE_SHIFT;

	return map_kernel_page(text_poke_addr, (pfn << PAGE_SHIFT), PAGE_KERNEL);
}

static void unmap_patch_area(unsigned long addr)
{
	pte_t *ptep;
	pmd_t *pmdp;
	pud_t *pudp;
	p4d_t *p4dp;
	pgd_t *pgdp;

	pgdp = pgd_offset_k(addr);
	if (WARN_ON(pgd_none(*pgdp)))
		return;

	p4dp = p4d_offset(pgdp, addr);
	if (WARN_ON(p4d_none(*p4dp)))
		return;

	pudp = pud_offset(p4dp, addr);
	if (WARN_ON(pud_none(*pudp)))
		return;

	pmdp = pmd_offset(pudp, addr);
	if (WARN_ON(pmd_none(*pmdp)))
		return;

	ptep = pte_offset_kernel(pmdp, addr);
	if (WARN_ON(pte_none(*ptep)))
		return;

	/*
	 * In hash, pte_clear flushes the tlb, in radix, we have to
	 */
	pte_clear(&init_mm, addr, ptep);
	flush_tlb_kernel_range(addr, addr + PAGE_SIZE);
}

static int __do_patch_instruction(u32 *addr, ppc_inst_t instr)
{
	int err;
	u32 *patch_addr;
	unsigned long text_poke_addr;

	text_poke_addr = (unsigned long)__this_cpu_read(text_poke_area)->addr;
	patch_addr = (u32 *)(text_poke_addr + offset_in_page(addr));

	err = map_patch_area(addr, text_poke_addr);
	if (err)
		return err;

	err = __patch_instruction(addr, instr, patch_addr);

	unmap_patch_area(text_poke_addr);

	return err;
}

static int do_patch_instruction(u32 *addr, ppc_inst_t instr)
{
	int err;
	unsigned long flags;

	/*
	 * During early early boot patch_instruction is called
	 * when text_poke_area is not ready, but we still need
	 * to allow patching. We just do the plain old patching
	 */
	if (!this_cpu_read(text_poke_area))
		return raw_patch_instruction(addr, instr);

	local_irq_save(flags);
	err = __do_patch_instruction(addr, instr);
	local_irq_restore(flags);

	return err;
}
#else /* !CONFIG_STRICT_KERNEL_RWX */

static int do_patch_instruction(u32 *addr, ppc_inst_t instr)
{
	return raw_patch_instruction(addr, instr);
}

#endif /* CONFIG_STRICT_KERNEL_RWX */

int patch_instruction(u32 *addr, ppc_inst_t instr)
{
	/* Make sure we aren't patching a freed init section */
	if (system_state >= SYSTEM_FREEING_INITMEM && init_section_contains(addr, 4))
		return 0;

	return do_patch_instruction(addr, instr);
}
NOKPROBE_SYMBOL(patch_instruction);

int patch_branch(u32 *addr, unsigned long target, int flags)
{
	ppc_inst_t instr;

	if (create_branch(&instr, addr, target, flags))
		return -ERANGE;

	return patch_instruction(addr, instr);
}

bool is_offset_in_branch_range(long offset)
{
	/*
	 * Powerpc branch instruction is :
	 *
	 *  0         6                 30   31
	 *  +---------+----------------+---+---+
	 *  | opcode  |     LI         |AA |LK |
	 *  +---------+----------------+---+---+
	 *  Where AA = 0 and LK = 0
	 *
	 * LI is a signed 24 bits integer. The real branch offset is computed
	 * by: imm32 = SignExtend(LI:'0b00', 32);
	 *
	 * So the maximum forward branch should be:
	 *   (0x007fffff << 2) = 0x01fffffc =  0x1fffffc
	 * The maximum backward branch should be:
	 *   (0xff800000 << 2) = 0xfe000000 = -0x2000000
	 */
	return (offset >= -0x2000000 && offset <= 0x1fffffc && !(offset & 0x3));
}

bool is_offset_in_cond_branch_range(long offset)
{
	return offset >= -0x8000 && offset <= 0x7fff && !(offset & 0x3);
}

/*
 * Helper to check if a given instruction is a conditional branch
 * Derived from the conditional checks in analyse_instr()
 */
bool is_conditional_branch(ppc_inst_t instr)
{
	unsigned int opcode = ppc_inst_primary_opcode(instr);

	if (opcode == 16)       /* bc, bca, bcl, bcla */
		return true;
	if (opcode == 19) {
		switch ((ppc_inst_val(instr) >> 1) & 0x3ff) {
		case 16:        /* bclr, bclrl */
		case 528:       /* bcctr, bcctrl */
		case 560:       /* bctar, bctarl */
			return true;
		}
	}
	return false;
}
NOKPROBE_SYMBOL(is_conditional_branch);

int create_branch(ppc_inst_t *instr, const u32 *addr,
		  unsigned long target, int flags)
{
	long offset;

	*instr = ppc_inst(0);
	offset = target;
	if (! (flags & BRANCH_ABSOLUTE))
		offset = offset - (unsigned long)addr;

	/* Check we can represent the target in the instruction format */
	if (!is_offset_in_branch_range(offset))
		return 1;

	/* Mask out the flags and target, so they don't step on each other. */
	*instr = ppc_inst(0x48000000 | (flags & 0x3) | (offset & 0x03FFFFFC));

	return 0;
}

int create_cond_branch(ppc_inst_t *instr, const u32 *addr,
		       unsigned long target, int flags)
{
	long offset;

	offset = target;
	if (! (flags & BRANCH_ABSOLUTE))
		offset = offset - (unsigned long)addr;

	/* Check we can represent the target in the instruction format */
	if (!is_offset_in_cond_branch_range(offset))
		return 1;

	/* Mask out the flags and target, so they don't step on each other. */
	*instr = ppc_inst(0x40000000 | (flags & 0x3FF0003) | (offset & 0xFFFC));

	return 0;
}

static unsigned int branch_opcode(ppc_inst_t instr)
{
	return ppc_inst_primary_opcode(instr) & 0x3F;
}

static int instr_is_branch_iform(ppc_inst_t instr)
{
	return branch_opcode(instr) == 18;
}

static int instr_is_branch_bform(ppc_inst_t instr)
{
	return branch_opcode(instr) == 16;
}

int instr_is_relative_branch(ppc_inst_t instr)
{
	if (ppc_inst_val(instr) & BRANCH_ABSOLUTE)
		return 0;

	return instr_is_branch_iform(instr) || instr_is_branch_bform(instr);
}

int instr_is_relative_link_branch(ppc_inst_t instr)
{
	return instr_is_relative_branch(instr) && (ppc_inst_val(instr) & BRANCH_SET_LINK);
}

static unsigned long branch_iform_target(const u32 *instr)
{
	signed long imm;

	imm = ppc_inst_val(ppc_inst_read(instr)) & 0x3FFFFFC;

	/* If the top bit of the immediate value is set this is negative */
	if (imm & 0x2000000)
		imm -= 0x4000000;

	if ((ppc_inst_val(ppc_inst_read(instr)) & BRANCH_ABSOLUTE) == 0)
		imm += (unsigned long)instr;

	return (unsigned long)imm;
}

static unsigned long branch_bform_target(const u32 *instr)
{
	signed long imm;

	imm = ppc_inst_val(ppc_inst_read(instr)) & 0xFFFC;

	/* If the top bit of the immediate value is set this is negative */
	if (imm & 0x8000)
		imm -= 0x10000;

	if ((ppc_inst_val(ppc_inst_read(instr)) & BRANCH_ABSOLUTE) == 0)
		imm += (unsigned long)instr;

	return (unsigned long)imm;
}

unsigned long branch_target(const u32 *instr)
{
	if (instr_is_branch_iform(ppc_inst_read(instr)))
		return branch_iform_target(instr);
	else if (instr_is_branch_bform(ppc_inst_read(instr)))
		return branch_bform_target(instr);

	return 0;
}

int translate_branch(ppc_inst_t *instr, const u32 *dest, const u32 *src)
{
	unsigned long target;
	target = branch_target(src);

	if (instr_is_branch_iform(ppc_inst_read(src)))
		return create_branch(instr, dest, target,
				     ppc_inst_val(ppc_inst_read(src)));
	else if (instr_is_branch_bform(ppc_inst_read(src)))
		return create_cond_branch(instr, dest, target,
					  ppc_inst_val(ppc_inst_read(src)));

	return 1;
}

#ifdef CONFIG_CODE_PATCHING_SELFTEST

static int __init instr_is_branch_to_addr(const u32 *instr, unsigned long addr)
{
	if (instr_is_branch_iform(ppc_inst_read(instr)) ||
	    instr_is_branch_bform(ppc_inst_read(instr)))
		return branch_target(instr) == addr;

	return 0;
}

static void __init test_trampoline(void)
{
	asm ("nop;nop;\n");
}

#define check(x)	do {	\
	if (!(x))		\
		pr_err("code-patching: test failed at line %d\n", __LINE__); \
} while (0)

static void __init test_branch_iform(void)
{
	int err;
	ppc_inst_t instr;
	u32 tmp[2];
	u32 *iptr = tmp;
	unsigned long addr = (unsigned long)tmp;

	/* The simplest case, branch to self, no flags */
	check(instr_is_branch_iform(ppc_inst(0x48000000)));
	/* All bits of target set, and flags */
	check(instr_is_branch_iform(ppc_inst(0x4bffffff)));
	/* High bit of opcode set, which is wrong */
	check(!instr_is_branch_iform(ppc_inst(0xcbffffff)));
	/* Middle bits of opcode set, which is wrong */
	check(!instr_is_branch_iform(ppc_inst(0x7bffffff)));

	/* Simplest case, branch to self with link */
	check(instr_is_branch_iform(ppc_inst(0x48000001)));
	/* All bits of targets set */
	check(instr_is_branch_iform(ppc_inst(0x4bfffffd)));
	/* Some bits of targets set */
	check(instr_is_branch_iform(ppc_inst(0x4bff00fd)));
	/* Must be a valid branch to start with */
	check(!instr_is_branch_iform(ppc_inst(0x7bfffffd)));

	/* Absolute branch to 0x100 */
	patch_instruction(iptr, ppc_inst(0x48000103));
	check(instr_is_branch_to_addr(iptr, 0x100));
	/* Absolute branch to 0x420fc */
	patch_instruction(iptr, ppc_inst(0x480420ff));
	check(instr_is_branch_to_addr(iptr, 0x420fc));
	/* Maximum positive relative branch, + 20MB - 4B */
	patch_instruction(iptr, ppc_inst(0x49fffffc));
	check(instr_is_branch_to_addr(iptr, addr + 0x1FFFFFC));
	/* Smallest negative relative branch, - 4B */
	patch_instruction(iptr, ppc_inst(0x4bfffffc));
	check(instr_is_branch_to_addr(iptr, addr - 4));
	/* Largest negative relative branch, - 32 MB */
	patch_instruction(iptr, ppc_inst(0x4a000000));
	check(instr_is_branch_to_addr(iptr, addr - 0x2000000));

	/* Branch to self, with link */
	err = create_branch(&instr, iptr, addr, BRANCH_SET_LINK);
	patch_instruction(iptr, instr);
	check(instr_is_branch_to_addr(iptr, addr));

	/* Branch to self - 0x100, with link */
	err = create_branch(&instr, iptr, addr - 0x100, BRANCH_SET_LINK);
	patch_instruction(iptr, instr);
	check(instr_is_branch_to_addr(iptr, addr - 0x100));

	/* Branch to self + 0x100, no link */
	err = create_branch(&instr, iptr, addr + 0x100, 0);
	patch_instruction(iptr, instr);
	check(instr_is_branch_to_addr(iptr, addr + 0x100));

	/* Maximum relative negative offset, - 32 MB */
	err = create_branch(&instr, iptr, addr - 0x2000000, BRANCH_SET_LINK);
	patch_instruction(iptr, instr);
	check(instr_is_branch_to_addr(iptr, addr - 0x2000000));

	/* Out of range relative negative offset, - 32 MB + 4*/
	err = create_branch(&instr, iptr, addr - 0x2000004, BRANCH_SET_LINK);
	check(err);

	/* Out of range relative positive offset, + 32 MB */
	err = create_branch(&instr, iptr, addr + 0x2000000, BRANCH_SET_LINK);
	check(err);

	/* Unaligned target */
	err = create_branch(&instr, iptr, addr + 3, BRANCH_SET_LINK);
	check(err);

	/* Check flags are masked correctly */
	err = create_branch(&instr, iptr, addr, 0xFFFFFFFC);
	patch_instruction(iptr, instr);
	check(instr_is_branch_to_addr(iptr, addr));
	check(ppc_inst_equal(instr, ppc_inst(0x48000000)));
}

static void __init test_create_function_call(void)
{
	u32 *iptr;
	unsigned long dest;
	ppc_inst_t instr;

	/* Check we can create a function call */
	iptr = (u32 *)ppc_function_entry(test_trampoline);
	dest = ppc_function_entry(test_create_function_call);
	create_branch(&instr, iptr, dest, BRANCH_SET_LINK);
	patch_instruction(iptr, instr);
	check(instr_is_branch_to_addr(iptr, dest));
}

static void __init test_branch_bform(void)
{
	int err;
	unsigned long addr;
	ppc_inst_t instr;
	u32 tmp[2];
	u32 *iptr = tmp;
	unsigned int flags;

	addr = (unsigned long)iptr;

	/* The simplest case, branch to self, no flags */
	check(instr_is_branch_bform(ppc_inst(0x40000000)));
	/* All bits of target set, and flags */
	check(instr_is_branch_bform(ppc_inst(0x43ffffff)));
	/* High bit of opcode set, which is wrong */
	check(!instr_is_branch_bform(ppc_inst(0xc3ffffff)));
	/* Middle bits of opcode set, which is wrong */
	check(!instr_is_branch_bform(ppc_inst(0x7bffffff)));

	/* Absolute conditional branch to 0x100 */
	patch_instruction(iptr, ppc_inst(0x43ff0103));
	check(instr_is_branch_to_addr(iptr, 0x100));
	/* Absolute conditional branch to 0x20fc */
	patch_instruction(iptr, ppc_inst(0x43ff20ff));
	check(instr_is_branch_to_addr(iptr, 0x20fc));
	/* Maximum positive relative conditional branch, + 32 KB - 4B */
	patch_instruction(iptr, ppc_inst(0x43ff7ffc));
	check(instr_is_branch_to_addr(iptr, addr + 0x7FFC));
	/* Smallest negative relative conditional branch, - 4B */
	patch_instruction(iptr, ppc_inst(0x43fffffc));
	check(instr_is_branch_to_addr(iptr, addr - 4));
	/* Largest negative relative conditional branch, - 32 KB */
	patch_instruction(iptr, ppc_inst(0x43ff8000));
	check(instr_is_branch_to_addr(iptr, addr - 0x8000));

	/* All condition code bits set & link */
	flags = 0x3ff000 | BRANCH_SET_LINK;

	/* Branch to self */
	err = create_cond_branch(&instr, iptr, addr, flags);
	patch_instruction(iptr, instr);
	check(instr_is_branch_to_addr(iptr, addr));

	/* Branch to self - 0x100 */
	err = create_cond_branch(&instr, iptr, addr - 0x100, flags);
	patch_instruction(iptr, instr);
	check(instr_is_branch_to_addr(iptr, addr - 0x100));

	/* Branch to self + 0x100 */
	err = create_cond_branch(&instr, iptr, addr + 0x100, flags);
	patch_instruction(iptr, instr);
	check(instr_is_branch_to_addr(iptr, addr + 0x100));

	/* Maximum relative negative offset, - 32 KB */
	err = create_cond_branch(&instr, iptr, addr - 0x8000, flags);
	patch_instruction(iptr, instr);
	check(instr_is_branch_to_addr(iptr, addr - 0x8000));

	/* Out of range relative negative offset, - 32 KB + 4*/
	err = create_cond_branch(&instr, iptr, addr - 0x8004, flags);
	check(err);

	/* Out of range relative positive offset, + 32 KB */
	err = create_cond_branch(&instr, iptr, addr + 0x8000, flags);
	check(err);

	/* Unaligned target */
	err = create_cond_branch(&instr, iptr, addr + 3, flags);
	check(err);

	/* Check flags are masked correctly */
	err = create_cond_branch(&instr, iptr, addr, 0xFFFFFFFC);
	patch_instruction(iptr, instr);
	check(instr_is_branch_to_addr(iptr, addr));
	check(ppc_inst_equal(instr, ppc_inst(0x43FF0000)));
}

static void __init test_translate_branch(void)
{
	unsigned long addr;
	void *p, *q;
	ppc_inst_t instr;
	void *buf;

	buf = vmalloc(PAGE_ALIGN(0x2000000 + 1));
	check(buf);
	if (!buf)
		return;

	/* Simple case, branch to self moved a little */
	p = buf;
	addr = (unsigned long)p;
	patch_branch(p, addr, 0);
	check(instr_is_branch_to_addr(p, addr));
	q = p + 4;
	translate_branch(&instr, q, p);
	patch_instruction(q, instr);
	check(instr_is_branch_to_addr(q, addr));

	/* Maximum negative case, move b . to addr + 32 MB */
	p = buf;
	addr = (unsigned long)p;
	patch_branch(p, addr, 0);
	q = buf + 0x2000000;
	translate_branch(&instr, q, p);
	patch_instruction(q, instr);
	check(instr_is_branch_to_addr(p, addr));
	check(instr_is_branch_to_addr(q, addr));
	check(ppc_inst_equal(ppc_inst_read(q), ppc_inst(0x4a000000)));

	/* Maximum positive case, move x to x - 32 MB + 4 */
	p = buf + 0x2000000;
	addr = (unsigned long)p;
	patch_branch(p, addr, 0);
	q = buf + 4;
	translate_branch(&instr, q, p);
	patch_instruction(q, instr);
	check(instr_is_branch_to_addr(p, addr));
	check(instr_is_branch_to_addr(q, addr));
	check(ppc_inst_equal(ppc_inst_read(q), ppc_inst(0x49fffffc)));

	/* Jump to x + 16 MB moved to x + 20 MB */
	p = buf;
	addr = 0x1000000 + (unsigned long)buf;
	patch_branch(p, addr, BRANCH_SET_LINK);
	q = buf + 0x1400000;
	translate_branch(&instr, q, p);
	patch_instruction(q, instr);
	check(instr_is_branch_to_addr(p, addr));
	check(instr_is_branch_to_addr(q, addr));

	/* Jump to x + 16 MB moved to x - 16 MB + 4 */
	p = buf + 0x1000000;
	addr = 0x2000000 + (unsigned long)buf;
	patch_branch(p, addr, 0);
	q = buf + 4;
	translate_branch(&instr, q, p);
	patch_instruction(q, instr);
	check(instr_is_branch_to_addr(p, addr));
	check(instr_is_branch_to_addr(q, addr));


	/* Conditional branch tests */

	/* Simple case, branch to self moved a little */
	p = buf;
	addr = (unsigned long)p;
	create_cond_branch(&instr, p, addr, 0);
	patch_instruction(p, instr);
	check(instr_is_branch_to_addr(p, addr));
	q = buf + 4;
	translate_branch(&instr, q, p);
	patch_instruction(q, instr);
	check(instr_is_branch_to_addr(q, addr));

	/* Maximum negative case, move b . to addr + 32 KB */
	p = buf;
	addr = (unsigned long)p;
	create_cond_branch(&instr, p, addr, 0xFFFFFFFC);
	patch_instruction(p, instr);
	q = buf + 0x8000;
	translate_branch(&instr, q, p);
	patch_instruction(q, instr);
	check(instr_is_branch_to_addr(p, addr));
	check(instr_is_branch_to_addr(q, addr));
	check(ppc_inst_equal(ppc_inst_read(q), ppc_inst(0x43ff8000)));

	/* Maximum positive case, move x to x - 32 KB + 4 */
	p = buf + 0x8000;
	addr = (unsigned long)p;
	create_cond_branch(&instr, p, addr, 0xFFFFFFFC);
	patch_instruction(p, instr);
	q = buf + 4;
	translate_branch(&instr, q, p);
	patch_instruction(q, instr);
	check(instr_is_branch_to_addr(p, addr));
	check(instr_is_branch_to_addr(q, addr));
	check(ppc_inst_equal(ppc_inst_read(q), ppc_inst(0x43ff7ffc)));

	/* Jump to x + 12 KB moved to x + 20 KB */
	p = buf;
	addr = 0x3000 + (unsigned long)buf;
	create_cond_branch(&instr, p, addr, BRANCH_SET_LINK);
	patch_instruction(p, instr);
	q = buf + 0x5000;
	translate_branch(&instr, q, p);
	patch_instruction(q, instr);
	check(instr_is_branch_to_addr(p, addr));
	check(instr_is_branch_to_addr(q, addr));

	/* Jump to x + 8 KB moved to x - 8 KB + 4 */
	p = buf + 0x2000;
	addr = 0x4000 + (unsigned long)buf;
	create_cond_branch(&instr, p, addr, 0);
	patch_instruction(p, instr);
	q = buf + 4;
	translate_branch(&instr, q, p);
	patch_instruction(q, instr);
	check(instr_is_branch_to_addr(p, addr));
	check(instr_is_branch_to_addr(q, addr));

	/* Free the buffer we were using */
	vfree(buf);
}

static void __init test_prefixed_patching(void)
{
	u32 *iptr = (u32 *)ppc_function_entry(test_trampoline);
	u32 expected[2] = {OP_PREFIX << 26, 0};
	ppc_inst_t inst = ppc_inst_prefix(OP_PREFIX << 26, 0);

	if (!IS_ENABLED(CONFIG_PPC64))
		return;

	patch_instruction(iptr, inst);

	check(!memcmp(iptr, expected, sizeof(expected)));
}

static int __init test_code_patching(void)
{
	pr_info("Running code patching self-tests ...\n");

	test_branch_iform();
	test_branch_bform();
	test_create_function_call();
	test_translate_branch();
	test_prefixed_patching();

	return 0;
}
late_initcall(test_code_patching);

#endif /* CONFIG_CODE_PATCHING_SELFTEST */