| Message ID | 20220922210320.1076658-5-jolsa@kernel.org (mailing list archive) |
|---|---|
| State | Superseded |
| Delegated to: | BPF |
| Headers | show |
| Series | bpf: Fixes for CONFIG_X86_KERNEL_IBT | expand |
On Thu, Sep 22, 2022 at 2:04 PM Jiri Olsa <jolsa@kernel.org> wrote: > > 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 7f0059b58f02 ("selftests/bpf: Fix kprobe_multi test.") > > Cc: Peter Zijlstra <peterz@infradead.org> > Reported-by: Martynas Pumputis <m@lambda.lt> > Signed-off-by: Jiri Olsa <jolsa@kernel.org> > --- lgtm Acked-by: Andrii Nakryiko <andrii@kernel.org> > kernel/trace/bpf_trace.c | 20 +++++++++++++++++-- > .../selftests/bpf/progs/kprobe_multi.c | 4 +--- > 2 files changed, 19 insertions(+), 5 deletions(-) > [...]
diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c index b05f0310dbd3..ebd1b348beb3 100644 --- a/kernel/trace/bpf_trace.c +++ b/kernel/trace/bpf_trace.c @@ -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) diff --git a/tools/testing/selftests/bpf/progs/kprobe_multi.c b/tools/testing/selftests/bpf/progs/kprobe_multi.c index 08f95a8155d1..98c3399e15c0 100644 --- a/tools/testing/selftests/bpf/progs/kprobe_multi.c +++ b/tools/testing/selftests/bpf/progs/kprobe_multi.c @@ -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) && \
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 7f0059b58f02 ("selftests/bpf: Fix kprobe_multi test.") Cc: Peter Zijlstra <peterz@infradead.org> Reported-by: Martynas Pumputis <m@lambda.lt> Signed-off-by: Jiri Olsa <jolsa@kernel.org> --- kernel/trace/bpf_trace.c | 20 +++++++++++++++++-- .../selftests/bpf/progs/kprobe_multi.c | 4 +--- 2 files changed, 19 insertions(+), 5 deletions(-)