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Commit 5a3ae7b3 authored by Ard Biesheuvel's avatar Ard Biesheuvel Committed by Will Deacon
Browse files

arm64/ftrace: fix inadvertent BUG() in trampoline check 



The ftrace trampoline code (which deals with modules loaded out of
BL range of the core kernel) uses plt_entries_equal() to check whether
the per-module trampoline equals a zero buffer, to decide whether the
trampoline has already been initialized.

This triggers a BUG() in the opcode manipulation code, since we end
up checking the ADRP offset of a 0x0 opcode, which is not an ADRP
instruction.

So instead, add a helper to check whether a PLT is initialized, and
call that from the frace code.

Cc: <stable@vger.kernel.org> # v5.0
Fixes: bdb85cd1 ("arm64/module: switch to ADRP/ADD sequences for PLT entries")
Acked-by: default avatarMark Rutland <mark.rutland@arm.com>
Signed-off-by: default avatarArd Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: default avatarWill Deacon <will.deacon@arm.com>
parent 15ade5d2

arch/arm64/include/asm/module.h

+5 −0
Original line number Diff line number Diff line
@@ -73,4 +73,9 @@ static inline bool is_forbidden_offset_for_adrp(void *place) 
struct plt_entry get_plt_entry(u64 dst, void *pc);

bool plt_entries_equal(const struct plt_entry *a, const struct plt_entry *b);



static inline bool plt_entry_is_initialized(const struct plt_entry *e)

{

	return e->adrp || e->add || e->br;

}



#endif /* __ASM_MODULE_H */

arch/arm64/kernel/ftrace.c

+1 −2
Original line number Diff line number Diff line
@@ -107,8 +107,7 @@ int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr) 
		trampoline = get_plt_entry(addr, mod->arch.ftrace_trampoline);

		if (!plt_entries_equal(mod->arch.ftrace_trampoline,

				       &trampoline)) {

			if (!plt_entries_equal(mod->arch.ftrace_trampoline,

					       &(struct plt_entry){})) {

			if (plt_entry_is_initialized(mod->arch.ftrace_trampoline)) {

				pr_err("ftrace: far branches to multiple entry points unsupported inside a single module\n");

				return -EINVAL;

			}