Commit 8486e54d authored Jun 23, 2017 by Mark Rutland Committed by Will Deacon Jun 23, 2017

arm64: ftrace: fix !CONFIG_ARM64_MODULE_PLTS kernels



When a kernel is built without CONFIG_ARM64_MODULE_PLTS, we don't
generate the expected branch instruction in ftrace_make_nop(). This
means we pass zero (rather than a valid branch) to ftrace_modify_code()
as the expected instruction to validate. This causes us to return
-EINVAL to the core ftrace code for a valid case, resulting in a splat
at boot time.

This was an unintended effect of commit:

  68764420 ("arm64: ftrace: fix building without CONFIG_MODULES")

... which incorrectly moved the generation of the branch instruction
into the ifdef for CONFIG_ARM64_MODULE_PLTS.

This patch fixes the issue by moving the ifdef inside of the relevant
if-else case, and always checking that the branch is in range,
regardless of CONFIG_ARM64_MODULE_PLTS. This ensures that we generate
the expected branch instruction, and also improves our sanity checks.

For consistency, both ftrace_make_nop() and ftrace_make_call() are
updated with this pattern.

Fixes: 68764420 ("arm64: ftrace: fix building without CONFIG_MODULES")
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Reported-by: Marc Zyngier <marc.zyngier@arm.com>
Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>

parent 33f08261

arch/arm64/kernel/ftrace.c

+8 −6

Original line number	Diff line number	Diff line
		@@ -72,11 +72,10 @@ int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
		{
		unsigned long pc = rec->ip;
		u32 old, new;

		#ifdef CONFIG_ARM64_MODULE_PLTS
		long offset = (long)pc - (long)addr;

		if (offset < -SZ_128M \|\| offset >= SZ_128M) {
		#ifdef CONFIG_ARM64_MODULE_PLTS
		unsigned long *trampoline;
		struct module *mod;

		@@ -121,8 +120,10 @@ int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
		smp_wmb();
		}
		addr = (unsigned long)&trampoline[1];
		}
		#else /* CONFIG_ARM64_MODULE_PLTS */
		return -EINVAL;
		#endif /* CONFIG_ARM64_MODULE_PLTS */
		}

		old = aarch64_insn_gen_nop();
		new = aarch64_insn_gen_branch_imm(pc, addr, AARCH64_INSN_BRANCH_LINK);
		@@ -139,11 +140,10 @@ int ftrace_make_nop(struct module mod, struct dyn_ftrace rec,
		unsigned long pc = rec->ip;
		bool validate = true;
		u32 old = 0, new;

		#ifdef CONFIG_ARM64_MODULE_PLTS
		long offset = (long)pc - (long)addr;

		if (offset < -SZ_128M \|\| offset >= SZ_128M) {
		#ifdef CONFIG_ARM64_MODULE_PLTS
		u32 replaced;

		/*
		@@ -176,11 +176,13 @@ int ftrace_make_nop(struct module mod, struct dyn_ftrace rec,
		return -EINVAL;

		validate = false;
		#else /* CONFIG_ARM64_MODULE_PLTS */
		return -EINVAL;
		#endif /* CONFIG_ARM64_MODULE_PLTS */
		} else {
		old = aarch64_insn_gen_branch_imm(pc, addr,
		AARCH64_INSN_BRANCH_LINK);
		}
		#endif /* CONFIG_ARM64_MODULE_PLTS */

		new = aarch64_insn_gen_nop();