From: Mark Rutland mark.rutland@arm.com
[ Upstream commit 8cfb08575c6d4585f1ce0deeb189e5c824776b04 ]
Li Huafei reports that mcount-based ftrace with module PLTs was broken by commit:
a6253579977e4c6f ("arm64: ftrace: consistently handle PLTs.")
When a module PLTs are used and a module is loaded sufficiently far away from the kernel, we'll create PLTs for any branches which are out-of-range. These are separate from the special ftrace trampoline PLTs, which the module PLT code doesn't directly manipulate.
When mcount is in use this is a problem, as each mcount callsite in a module will be initialized to point to a module PLT, but since commit a6253579977e4c6f ftrace_make_nop() will assume that the callsite has been initialized to point to the special ftrace trampoline PLT, and ftrace_find_callable_addr() rejects other cases.
This means that when ftrace tries to initialize a callsite via ftrace_make_nop(), the call to ftrace_find_callable_addr() will find that the `_mcount` stub is out-of-range and is not handled by the ftrace PLT, resulting in a splat:
| ftrace_test: loading out-of-tree module taints kernel. | ftrace: no module PLT for _mcount | ------------[ ftrace bug ]------------ | ftrace failed to modify | [<ffff800029180014>] 0xffff800029180014 | actual: 44:00:00:94 | Initializing ftrace call sites | ftrace record flags: 2000000 | (0) | expected tramp: ffff80000802eb3c | ------------[ cut here ]------------ | WARNING: CPU: 3 PID: 157 at kernel/trace/ftrace.c:2120 ftrace_bug+0x94/0x270 | Modules linked in: | CPU: 3 PID: 157 Comm: insmod Tainted: G O 6.0.0-rc6-00151-gcd722513a189-dirty #22 | Hardware name: linux,dummy-virt (DT) | pstate: 60000005 (nZCv daif -PAN -UAO -TCO -DIT -SSBS BTYPE=--) | pc : ftrace_bug+0x94/0x270 | lr : ftrace_bug+0x21c/0x270 | sp : ffff80000b2bbaf0 | x29: ffff80000b2bbaf0 x28: 0000000000000000 x27: ffff0000c4d38000 | x26: 0000000000000001 x25: ffff800009d7e000 x24: ffff0000c4d86e00 | x23: 0000000002000000 x22: ffff80000a62b000 x21: ffff8000098ebea8 | x20: ffff0000c4d38000 x19: ffff80000aa24158 x18: ffffffffffffffff | x17: 0000000000000000 x16: 0a0d2d2d2d2d2d2d x15: ffff800009aa9118 | x14: 0000000000000000 x13: 6333626532303830 x12: 3030303866666666 | x11: 203a706d61727420 x10: 6465746365707865 x9 : 3362653230383030 | x8 : c0000000ffffefff x7 : 0000000000017fe8 x6 : 000000000000bff4 | x5 : 0000000000057fa8 x4 : 0000000000000000 x3 : 0000000000000001 | x2 : ad2cb14bb5438900 x1 : 0000000000000000 x0 : 0000000000000022 | Call trace: | ftrace_bug+0x94/0x270 | ftrace_process_locs+0x308/0x430 | ftrace_module_init+0x44/0x60 | load_module+0x15b4/0x1ce8 | __do_sys_init_module+0x1ec/0x238 | __arm64_sys_init_module+0x24/0x30 | invoke_syscall+0x54/0x118 | el0_svc_common.constprop.4+0x84/0x100 | do_el0_svc+0x3c/0xd0 | el0_svc+0x1c/0x50 | el0t_64_sync_handler+0x90/0xb8 | el0t_64_sync+0x15c/0x160 | ---[ end trace 0000000000000000 ]--- | ---------test_init-----------
Fix this by reverting to the old behaviour of ignoring the old instruction when initialising an mcount callsite in a module, which was the behaviour prior to commit a6253579977e4c6f.
Signed-off-by: Mark Rutland mark.rutland@arm.com Fixes: a6253579977e ("arm64: ftrace: consistently handle PLTs.") Reported-by: Li Huafei lihuafei1@huawei.com Link: https://lore.kernel.org/linux-arm-kernel/20220929094134.99512-1-lihuafei1@hu... Cc: Ard Biesheuvel ardb@kernel.org Cc: Will Deacon will@kernel.org Link: https://lore.kernel.org/r/20220929134525.798593-1-mark.rutland@arm.com Signed-off-by: Catalin Marinas catalin.marinas@arm.com Signed-off-by: Sasha Levin sashal@kernel.org --- arch/arm64/kernel/ftrace.c | 17 ++++++++++++++++- 1 file changed, 16 insertions(+), 1 deletion(-)
diff --git a/arch/arm64/kernel/ftrace.c b/arch/arm64/kernel/ftrace.c index ea5dc7c90f46..b49ba9a24bcc 100644 --- a/arch/arm64/kernel/ftrace.c +++ b/arch/arm64/kernel/ftrace.c @@ -217,11 +217,26 @@ int ftrace_make_nop(struct module *mod, struct dyn_ftrace *rec, unsigned long pc = rec->ip; u32 old = 0, new;
+ new = aarch64_insn_gen_nop(); + + /* + * When using mcount, callsites in modules may have been initalized to + * call an arbitrary module PLT (which redirects to the _mcount stub) + * rather than the ftrace PLT we'll use at runtime (which redirects to + * the ftrace trampoline). We can ignore the old PLT when initializing + * the callsite. + * + * Note: 'mod' is only set at module load time. + */ + if (!IS_ENABLED(CONFIG_DYNAMIC_FTRACE_WITH_REGS) && + IS_ENABLED(CONFIG_ARM64_MODULE_PLTS) && mod) { + return aarch64_insn_patch_text_nosync((void *)pc, new); + } + if (!ftrace_find_callable_addr(rec, mod, &addr)) return -EINVAL;
old = aarch64_insn_gen_branch_imm(pc, addr, AARCH64_INSN_BRANCH_LINK); - new = aarch64_insn_gen_nop();
return ftrace_modify_code(pc, old, new, true); }