From: Ard Biesheuvel <[email protected]> commit 5a3ae7b314a2259b1188b22b392f5eba01e443ee upstream.
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: <[email protected]> # v5.0 Fixes: bdb85cd1d206 ("arm64/module: switch to ADRP/ADD sequences for PLT entries") Acked-by: Mark Rutland <[email protected]> Signed-off-by: Ard Biesheuvel <[email protected]> Signed-off-by: Will Deacon <[email protected]> Signed-off-by: Greg Kroah-Hartman <[email protected]> --- arch/arm64/include/asm/module.h | 5 +++++ arch/arm64/kernel/ftrace.c | 3 +-- 2 files changed, 6 insertions(+), 2 deletions(-) --- a/arch/arm64/include/asm/module.h +++ b/arch/arm64/include/asm/module.h @@ -73,4 +73,9 @@ static inline bool is_forbidden_offset_f 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 */ --- a/arch/arm64/kernel/ftrace.c +++ b/arch/arm64/kernel/ftrace.c @@ -107,8 +107,7 @@ int ftrace_make_call(struct dyn_ftrace * 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; }
