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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 7f0059b58f ("selftests/bpf: Fix kprobe_multi test.")

Cc: Peter Zijlstra <peterz@infradead.org>
Reported-by: Martynas Pumputis <m@lambda.lt>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Link: https://lore.kernel.org/r/20220926153340.1621984-5-jolsa@kernel.org
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
Jiri Olsa 2022-09-26 17:33:38 +02:00 committed by Alexei Starovoitov
parent 4d854f4f31
commit c09eb2e578
2 changed files with 19 additions and 5 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

20
kernel/trace/bpf_trace.c
View File

@ -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)

4
tools/testing/selftests/bpf/progs/kprobe_multi.c
View File

@ -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) && \