From fa99a3470e917a7a83b0648b53d2e1a5d71f3b29 Mon Sep 17 00:00:00 2001 From: "Naveen N. Rao" Date: Wed, 17 Jan 2018 17:52:24 +0530 Subject: [PATCH] powerpc/kprobes: Fix call trace due to incorrect preempt count commit e6e133c47e6bd4d5dac05b35d06634a8e5648615 upstream. Michael Ellerman reported the following call trace when running ftracetest: BUG: using __this_cpu_write() in preemptible [00000000] code: ftracetest/6178 caller is opt_pre_handler+0xc4/0x110 CPU: 1 PID: 6178 Comm: ftracetest Not tainted 4.15.0-rc7-gcc6x-gb2cd1df #1 Call Trace: [c0000000f9ec39c0] [c000000000ac4304] dump_stack+0xb4/0x100 (unreliable) [c0000000f9ec3a00] [c00000000061159c] check_preemption_disabled+0x15c/0x170 [c0000000f9ec3a90] [c000000000217e84] opt_pre_handler+0xc4/0x110 [c0000000f9ec3af0] [c00000000004cf68] optimized_callback+0x148/0x170 [c0000000f9ec3b40] [c00000000004d954] optinsn_slot+0xec/0x10000 [c0000000f9ec3e30] [c00000000004bae0] kretprobe_trampoline+0x0/0x10 This is showing up since OPTPROBES is now enabled with CONFIG_PREEMPT. trampoline_probe_handler() considers itself to be a special kprobe handler for kretprobes. In doing so, it expects to be called from kprobe_handler() on a trap, and re-enables preemption before returning a non-zero return value so as to suppress any subsequent processing of the trap by the kprobe_handler(). However, with optprobes, we don't deal with special handlers (we ignore the return code) and just try to re-enable preemption causing the above trace. To address this, modify trampoline_probe_handler() to not be special. The only additional processing done in kprobe_handler() is to emulate the instruction (in this case, a 'nop'). We adjust the value of regs->nip for the purpose and delegate the job of re-enabling preemption and resetting current kprobe to the probe handlers (kprobe_handler() or optimized_callback()). Fixes: 8a2d71a3f273 ("powerpc/kprobes: Disable preemption before invoking probe handler for optprobes") Cc: stable@vger.kernel.org # v4.15+ Reported-by: Michael Ellerman Signed-off-by: Naveen N. Rao Acked-by: Ananth N Mavinakayanahalli Signed-off-by: Michael Ellerman Signed-off-by: Greg Kroah-Hartman --- arch/powerpc/kernel/kprobes.c | 30 +++++++++++++++++------------- 1 file changed, 17 insertions(+), 13 deletions(-) diff --git a/arch/powerpc/kernel/kprobes.c b/arch/powerpc/kernel/kprobes.c index bebc3007a793..10b46b35c059 100644 --- a/arch/powerpc/kernel/kprobes.c +++ b/arch/powerpc/kernel/kprobes.c @@ -457,29 +457,33 @@ static int trampoline_probe_handler(struct kprobe *p, struct pt_regs *regs) } kretprobe_assert(ri, orig_ret_address, trampoline_address); - regs->nip = orig_ret_address; + /* - * Make LR point to the orig_ret_address. - * When the 'nop' inside the kretprobe_trampoline - * is optimized, we can do a 'blr' after executing the - * detour buffer code. + * We get here through one of two paths: + * 1. by taking a trap -> kprobe_handler() -> here + * 2. by optprobe branch -> optimized_callback() -> opt_pre_handler() -> here + * + * When going back through (1), we need regs->nip to be setup properly + * as it is used to determine the return address from the trap. + * For (2), since nip is not honoured with optprobes, we instead setup + * the link register properly so that the subsequent 'blr' in + * kretprobe_trampoline jumps back to the right instruction. + * + * For nip, we should set the address to the previous instruction since + * we end up emulating it in kprobe_handler(), which increments the nip + * again. */ + regs->nip = orig_ret_address - 4; regs->link = orig_ret_address; - reset_current_kprobe(); kretprobe_hash_unlock(current, &flags); - preempt_enable_no_resched(); hlist_for_each_entry_safe(ri, tmp, &empty_rp, hlist) { hlist_del(&ri->hlist); kfree(ri); } - /* - * By returning a non-zero value, we are telling - * kprobe_handler() that we don't want the post_handler - * to run (and have re-enabled preemption) - */ - return 1; + + return 0; } NOKPROBE_SYMBOL(trampoline_probe_handler); -- 2.20.1