Commit c09eb2e5 authored by Jiri Olsa's avatar Jiri Olsa Committed by Alexei Starovoitov
Browse files

bpf: Adjust kprobe_multi entry_ip for CONFIG_X86_KERNEL_IBT 



Martynas reported bpf_get_func_ip returning +4 address when
CONFIG_X86_KERNEL_IBT option is enabled.

When CONFIG_X86_KERNEL_IBT is enabled we'll have endbr instruction
at the function entry, which screws return value of bpf_get_func_ip()
helper that should return the function address.

There's short term workaround for kprobe_multi bpf program made by
Alexei [1], but we need this fixup also for bpf_get_attach_cookie,
that returns cookie based on the entry_ip value.

Moving the fixup in the fprobe handler, so both bpf_get_func_ip
and bpf_get_attach_cookie get expected function address when
CONFIG_X86_KERNEL_IBT option is enabled.

Also renaming kprobe_multi_link_handler entry_ip argument to fentry_ip
so it's clearer this is an ftrace __fentry__ ip.

[1] commit 7f0059b5 ("selftests/bpf: Fix kprobe_multi test.")

Cc: Peter Zijlstra <peterz@infradead.org>
Reported-by: default avatarMartynas Pumputis <m@lambda.lt>
Acked-by: default avatarAndrii Nakryiko <andrii@kernel.org>
Signed-off-by: default avatarJiri Olsa <jolsa@kernel.org>
Link: https://lore.kernel.org/r/20220926153340.1621984-5-jolsa@kernel.org


Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
parent 4d854f4f

kernel/trace/bpf_trace.c

+18 −2
Original line number Diff line number Diff line
@@ -1028,6 +1028,22 @@ static const struct bpf_func_proto bpf_get_func_ip_proto_tracing = { 
	.arg1_type	= ARG_PTR_TO_CTX,

};



#ifdef CONFIG_X86_KERNEL_IBT

static unsigned long get_entry_ip(unsigned long fentry_ip)

{

	u32 instr;



	/* Being extra safe in here in case entry ip is on the page-edge. */

	if (get_kernel_nofault(instr, (u32 *) fentry_ip - 1))

		return fentry_ip;

	if (is_endbr(instr))

		fentry_ip -= ENDBR_INSN_SIZE;

	return fentry_ip;

}

#else

#define get_entry_ip(fentry_ip) fentry_ip

#endif



BPF_CALL_1(bpf_get_func_ip_kprobe, struct pt_regs *, regs)

{

	struct kprobe *kp = kprobe_running();
@@ -2600,13 +2616,13 @@ kprobe_multi_link_prog_run(struct bpf_kprobe_multi_link *link, 
}



static void

kprobe_multi_link_handler(struct fprobe *fp, unsigned long entry_ip,

kprobe_multi_link_handler(struct fprobe *fp, unsigned long fentry_ip,

			  struct pt_regs *regs)

{

	struct bpf_kprobe_multi_link *link;



	link = container_of(fp, struct bpf_kprobe_multi_link, fp);

	kprobe_multi_link_prog_run(link, entry_ip, regs);

	kprobe_multi_link_prog_run(link, get_entry_ip(fentry_ip), regs);

}



static int symbols_cmp_r(const void *a, const void *b, const void *priv)

tools/testing/selftests/bpf/progs/kprobe_multi.c

+1 −3
Original line number Diff line number Diff line
@@ -36,15 +36,13 @@ __u64 kretprobe_test6_result = 0; 
__u64 kretprobe_test7_result = 0;

__u64 kretprobe_test8_result = 0;



extern bool CONFIG_X86_KERNEL_IBT __kconfig __weak;



static void kprobe_multi_check(void *ctx, bool is_return)

{

	if (bpf_get_current_pid_tgid() >> 32 != pid)

		return;



	__u64 cookie = test_cookie ? bpf_get_attach_cookie(ctx) : 0;

	__u64 addr = bpf_get_func_ip(ctx) - (CONFIG_X86_KERNEL_IBT ? 4 : 0);

	__u64 addr = bpf_get_func_ip(ctx);



#define SET(__var, __addr, __cookie) ({			\

	if (((const void *) addr == __addr) &&		\