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author | Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com> | 2018-01-17 17:52:24 +0530 |
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committer | Michael Ellerman <mpe@ellerman.id.au> | 2018-03-31 00:10:33 +1100 |
commit | e6e133c47e6bd4d5dac05b35d06634a8e5648615 (patch) | |
tree | f5715986968854c86094882564eeb9121a90e3fe /arch/powerpc/kernel/kprobes.c | |
parent | 3a52f6f980c45b0dfa667f30d3ff034d033d260f (diff) | |
download | linux-e6e133c47e6bd4d5dac05b35d06634a8e5648615.tar.bz2 |
powerpc/kprobes: Fix call trace due to incorrect preempt count
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 <mpe@ellerman.id.au>
Signed-off-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
Acked-by: Ananth N Mavinakayanahalli <ananth@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Diffstat (limited to 'arch/powerpc/kernel/kprobes.c')
-rw-r--r-- | arch/powerpc/kernel/kprobes.c | 30 |
1 files changed, 17 insertions, 13 deletions
diff --git a/arch/powerpc/kernel/kprobes.c b/arch/powerpc/kernel/kprobes.c index ca5d5a081e75..e4c5bf33970b 100644 --- a/arch/powerpc/kernel/kprobes.c +++ b/arch/powerpc/kernel/kprobes.c @@ -455,29 +455,33 @@ 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); |