Commit 562bde0b authored by Naveen N Rao's avatar Naveen N Rao Committed by Michael Ellerman
Browse files

powerpc/ftrace: Simplify ftrace_make_nop() 



Now that we validate the ftrace location during initialization in
ftrace_init_nop(), we can simplify ftrace_make_nop() to patch-in the nop
without worrying about the instructions surrounding the ftrace location.
Note that we continue to ensure that we have a bl to
ftrace_[regs_]caller at the ftrace location before nop-ing it out.

Signed-off-by: default avatarNaveen N Rao <naveen@kernel.org>
Reviewed-by: default avatarChristophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: default avatarMichael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/e12ccbf28c50c3a07fb614f4d392e55f7098a729.1687166935.git.naveen@kernel.org
parent cc93b923

arch/powerpc/kernel/trace/ftrace.c

+32 −188
Original line number Diff line number Diff line
@@ -116,112 +116,6 @@ static unsigned long find_bl_target(unsigned long ip, ppc_inst_t op) 
	return ip + (long)offset;

}



#ifdef CONFIG_MODULES

static int

__ftrace_make_nop(struct module *mod,

		  struct dyn_ftrace *rec, unsigned long addr)

{

	unsigned long entry, ptr, tramp;

	unsigned long ip = rec->ip;

	ppc_inst_t op, pop;



	/* read where this goes */

	if (copy_inst_from_kernel_nofault(&op, (void *)ip)) {

		pr_err("Fetching opcode failed.\n");

		return -EFAULT;

	}



	/* Make sure that this is still a 24bit jump */

	if (!is_bl_op(op)) {

		pr_err("Not expected bl: opcode is %08lx\n", ppc_inst_as_ulong(op));

		return -EINVAL;

	}



	/* lets find where the pointer goes */

	tramp = find_bl_target(ip, op);



	pr_devel("ip:%lx jumps to %lx", ip, tramp);



	if (module_trampoline_target(mod, tramp, &ptr)) {

		pr_err("Failed to get trampoline target\n");

		return -EFAULT;

	}



	pr_devel("trampoline target %lx", ptr);



	entry = ppc_global_function_entry((void *)addr);

	/* This should match what was called */

	if (ptr != entry) {

		pr_err("addr %lx does not match expected %lx\n", ptr, entry);

		return -EINVAL;

	}



	if (IS_ENABLED(CONFIG_MPROFILE_KERNEL)) {

		if (copy_inst_from_kernel_nofault(&op, (void *)(ip - 4))) {

			pr_err("Fetching instruction at %lx failed.\n", ip - 4);

			return -EFAULT;

		}



		/* We expect either a mflr r0, or a std r0, LRSAVE(r1) */

		if (!ppc_inst_equal(op, ppc_inst(PPC_RAW_MFLR(_R0))) &&

		    !ppc_inst_equal(op, ppc_inst(PPC_INST_STD_LR))) {

			pr_err("Unexpected instruction %08lx around bl _mcount\n",

			       ppc_inst_as_ulong(op));

			return -EINVAL;

		}

	} else if (IS_ENABLED(CONFIG_PPC64)) {

		/*

		 * Check what is in the next instruction. We can see ld r2,40(r1), but

		 * on first pass after boot we will see mflr r0.

		 */

		if (copy_inst_from_kernel_nofault(&op, (void *)(ip + 4))) {

			pr_err("Fetching op failed.\n");

			return -EFAULT;

		}



		if (!ppc_inst_equal(op,  ppc_inst(PPC_INST_LD_TOC))) {

			pr_err("Expected %08lx found %08lx\n", PPC_INST_LD_TOC,

			       ppc_inst_as_ulong(op));

			return -EINVAL;

		}

	}



	/*

	 * When using -mprofile-kernel or PPC32 there is no load to jump over.

	 *

	 * Otherwise our original call site looks like:

	 *

	 * bl <tramp>

	 * ld r2,XX(r1)

	 *

	 * Milton Miller pointed out that we can not simply nop the branch.

	 * If a task was preempted when calling a trace function, the nops

	 * will remove the way to restore the TOC in r2 and the r2 TOC will

	 * get corrupted.

	 *

	 * Use a b +8 to jump over the load.

	 * XXX: could make PCREL depend on MPROFILE_KERNEL

	 * XXX: check PCREL && MPROFILE_KERNEL calling sequence

	 */

	if (IS_ENABLED(CONFIG_MPROFILE_KERNEL) || IS_ENABLED(CONFIG_PPC32))

		pop = ppc_inst(PPC_RAW_NOP());

	else

		pop = ppc_inst(PPC_RAW_BRANCH(8));	/* b +8 */



	if (patch_instruction((u32 *)ip, pop)) {

		pr_err("Patching NOP failed.\n");

		return -EPERM;

	}



	return 0;

}

#else

static int __ftrace_make_nop(struct module *mod, struct dyn_ftrace *rec, unsigned long addr)

{

	return 0;

}

#endif /* CONFIG_MODULES */



static unsigned long find_ftrace_tramp(unsigned long ip)

{

	int i;
@@ -235,88 +129,6 @@ static unsigned long find_ftrace_tramp(unsigned long ip) 
	return 0;

}



static int __ftrace_make_nop_kernel(struct dyn_ftrace *rec, unsigned long addr)

{

	unsigned long tramp, ip = rec->ip;

	ppc_inst_t op;



	/* Read where this goes */

	if (copy_inst_from_kernel_nofault(&op, (void *)ip)) {

		pr_err("Fetching opcode failed.\n");

		return -EFAULT;

	}



	/* Make sure that this is still a 24bit jump */

	if (!is_bl_op(op)) {

		pr_err("Not expected bl: opcode is %08lx\n", ppc_inst_as_ulong(op));

		return -EINVAL;

	}



	/* Let's find where the pointer goes */

	tramp = find_bl_target(ip, op);



	pr_devel("ip:%lx jumps to %lx", ip, tramp);



	/* Are ftrace trampolines reachable? */

	if (!find_ftrace_tramp(ip)) {

		pr_err("No ftrace trampolines reachable from %ps\n", (void *)ip);

		return -EINVAL;

	}



	if (patch_instruction((u32 *)ip, ppc_inst(PPC_RAW_NOP()))) {

		pr_err("Patching NOP failed.\n");

		return -EPERM;

	}



	return 0;

}



int ftrace_make_nop(struct module *mod,

		    struct dyn_ftrace *rec, unsigned long addr)

{

	unsigned long ip = rec->ip;

	ppc_inst_t old, new;



	/*

	 * If the calling address is more that 24 bits away,

	 * then we had to use a trampoline to make the call.

	 * Otherwise just update the call site.

	 */

	if (test_24bit_addr(ip, addr)) {

		/* within range */

		old = ftrace_call_replace(ip, addr, 1);

		new = ppc_inst(PPC_RAW_NOP());

		return ftrace_modify_code(ip, old, new);

	} else if (core_kernel_text(ip)) {

		return __ftrace_make_nop_kernel(rec, addr);

	} else if (!IS_ENABLED(CONFIG_MODULES)) {

		return -EINVAL;

	}



	/*

	 * Out of range jumps are called from modules.

	 * We should either already have a pointer to the module

	 * or it has been passed in.

	 */

	if (!rec->arch.mod) {

		if (!mod) {

			pr_err("No module loaded addr=%lx\n", addr);

			return -EFAULT;

		}

		rec->arch.mod = mod;

	} else if (mod) {

		if (mod != rec->arch.mod) {

			pr_err("Record mod %p not equal to passed in mod %p\n",

			       rec->arch.mod, mod);

			return -EINVAL;

		}

		/* nothing to do if mod == rec->arch.mod */

	} else

		mod = rec->arch.mod;



	return __ftrace_make_nop(mod, rec, addr);

}



#ifdef CONFIG_MODULES

/*

 * Examine the existing instructions for __ftrace_make_call.
@@ -607,6 +419,38 @@ int ftrace_modify_call(struct dyn_ftrace *rec, unsigned long old_addr, 
}

#endif



int ftrace_make_nop(struct module *mod, struct dyn_ftrace *rec, unsigned long addr)

{

	unsigned long tramp, ip = rec->ip;

	ppc_inst_t old, new;



	/* Nop-out the ftrace location */

	new = ppc_inst(PPC_RAW_NOP());

	if (is_offset_in_branch_range(addr - ip)) {

		/* Within range */

		old = ftrace_create_branch_inst(ip, addr, 1);

		return ftrace_modify_code(ip, old, new);

	} else if (core_kernel_text(ip)) {

		/* We would be branching to one of our ftrace tramps */

		tramp = find_ftrace_tramp(ip);

		if (!tramp) {

			pr_err("0x%lx: No ftrace trampolines reachable\n", ip);

			return -EINVAL;

		}

		old = ftrace_create_branch_inst(ip, tramp, 1);

		return ftrace_modify_code(ip, old, new);

	} else if (IS_ENABLED(CONFIG_MODULES)) {

		/* Module code would be going to one of the module stubs */

		if (!mod)

			mod = rec->arch.mod;

		tramp = (addr == (unsigned long)ftrace_caller ? mod->arch.tramp : mod->arch.tramp_regs);

		old = ftrace_create_branch_inst(ip, tramp, 1);

		return ftrace_modify_code(ip, old, new);

	}



	return -EINVAL;

}



int ftrace_init_nop(struct module *mod, struct dyn_ftrace *rec)

{

	unsigned long addr, ip = rec->ip;