| Message ID | 20200609081019.60234-3-sumanthk@linux.ibm.com |
|---|---|
| State | Not Applicable |
| Delegated to: | BPF Maintainers |
| Headers | show |
| Series | perf: Fix bpf prologue generation, uaccess | expand |
Em Tue, Jun 09, 2020 at 10:10:19AM +0200, Sumanth Korikkar escreveu: > Issue: > bpf_probe_read is no longer available for architecture which has > overlapping address space. Hence bpf prologue generation fails > > Fix: > Use bpf_probe_read_kernel for kernel member access. For user > attribute access in kprobes, use bpf_probe_read_user. > > Other: > @user attribute was introduced in commit 1e032f7cfa14 ("perf-probe: > Add user memory access attribute support") > > Test: > 1. ulimit -l 128 ; ./perf record -e tests/bpf_sched_setscheduler.c > 2. cat tests/bpf_sched_setscheduler.c > > static void (*bpf_trace_printk)(const char *fmt, int fmt_size, ...) = > (void *) 6; > static int (*bpf_probe_read_user)(void *dst, __u32 size, > const void *unsafe_ptr) = (void *) 112; > static int (*bpf_probe_read_kernel)(void *dst, __u32 size, > const void *unsafe_ptr) = (void *) 113; > > SEC("func=do_sched_setscheduler pid policy param->sched_priority@user") > int bpf_func__setscheduler(void *ctx, int err, pid_t pid, int policy, > int param) > { > char fmt[] = "prio: %ld"; > bpf_trace_printk(fmt, sizeof(fmt), param); > return 1; > } > > char _license[] SEC("license") = "GPL"; > int _version SEC("version") = LINUX_VERSION_CODE; > > 3. ./perf script > sched 305669 [000] 1614458.838675: perf_bpf_probe:func: (2904e508) > pid=261614 policy=2 sched_priority=1 > > 4. cat /sys/kernel/debug/tracing/trace > <...>-309956 [006] .... 1616098.093957: 0: prio: 1 Thanks for providing a detailed set of steps to test your patch, that is great! I added this, an alterenative way to test it, combining all the aspects in one 'perf trace' call: Committer testing: I had to add some missing headers in the bpf_sched_setscheduler.c test proggie, then instead of using record+script I used 'perf trace' to drive everything in one go: # cat bpf_sched_setscheduler.c #include <linux/types.h> #include <bpf.h> static void (*bpf_trace_printk)(const char *fmt, int fmt_size, ...) = (void *) 6; static int (*bpf_probe_read_user)(void *dst, __u32 size, const void *unsafe_ptr) = (void *) 112; static int (*bpf_probe_read_kernel)(void *dst, __u32 size, const void *unsafe_ptr) = (void *) 113; SEC("func=do_sched_setscheduler pid policy param->sched_priority@user") int bpf_func__setscheduler(void *ctx, int err, pid_t pid, int policy, int param) { char fmt[] = "prio: %ld"; bpf_trace_printk(fmt, sizeof(fmt), param); return 1; } char _license[] SEC("license") = "GPL"; int _version SEC("version") = LINUX_VERSION_CODE; # # # perf trace -e bpf_sched_setscheduler.c chrt -f 42 sleep 1 0.000 chrt/80125 perf_bpf_probe:func(__probe_ip: -1676607808, policy: 1, sched_priority: 42) # And even with backtraces :-) # perf trace -e bpf_sched_setscheduler.c/max-stack=8/ chrt -f 42 sleep 1 0.000 chrt/79805 perf_bpf_probe:func(__probe_ip: -1676607808, policy: 1, sched_priority: 42) do_sched_setscheduler ([kernel.kallsyms]) __x64_sys_sched_setscheduler ([kernel.kallsyms]) do_syscall_64 ([kernel.kallsyms]) entry_SYSCALL_64 ([kernel.kallsyms]) __GI___sched_setscheduler (/usr/lib64/libc-2.30.so) # - Arnaldo
diff --git a/tools/perf/util/bpf-prologue.c b/tools/perf/util/bpf-prologue.c index b020a8678eb9..9887ae09242d 100644 --- a/tools/perf/util/bpf-prologue.c +++ b/tools/perf/util/bpf-prologue.c @@ -142,7 +142,8 @@ static int gen_read_mem(struct bpf_insn_pos *pos, int src_base_addr_reg, int dst_addr_reg, - long offset) + long offset, + int probeid) { /* mov arg3, src_base_addr_reg */ if (src_base_addr_reg != BPF_REG_ARG3) @@ -159,7 +160,7 @@ gen_read_mem(struct bpf_insn_pos *pos, ins(BPF_MOV64_REG(BPF_REG_ARG1, dst_addr_reg), pos); /* Call probe_read */ - ins(BPF_EMIT_CALL(BPF_FUNC_probe_read), pos); + ins(BPF_EMIT_CALL(probeid), pos); /* * Error processing: if read fail, goto error code, * will be relocated. Target should be the start of @@ -241,7 +242,7 @@ static int gen_prologue_slowpath(struct bpf_insn_pos *pos, struct probe_trace_arg *args, int nargs) { - int err, i; + int err, i, probeid; for (i = 0; i < nargs; i++) { struct probe_trace_arg *arg = &args[i]; @@ -276,11 +277,16 @@ gen_prologue_slowpath(struct bpf_insn_pos *pos, stack_offset), pos); ref = arg->ref; + probeid = BPF_FUNC_probe_read_kernel; while (ref) { pr_debug("prologue: arg %d: offset %ld\n", i, ref->offset); + + if (ref->user_access) + probeid = BPF_FUNC_probe_read_user; + err = gen_read_mem(pos, BPF_REG_3, BPF_REG_7, - ref->offset); + ref->offset, probeid); if (err) { pr_err("prologue: failed to generate probe_read function call\n"); goto errout;
Issue: bpf_probe_read is no longer available for architecture which has overlapping address space. Hence bpf prologue generation fails Fix: Use bpf_probe_read_kernel for kernel member access. For user attribute access in kprobes, use bpf_probe_read_user. Other: @user attribute was introduced in commit 1e032f7cfa14 ("perf-probe: Add user memory access attribute support") Test: 1. ulimit -l 128 ; ./perf record -e tests/bpf_sched_setscheduler.c 2. cat tests/bpf_sched_setscheduler.c static void (*bpf_trace_printk)(const char *fmt, int fmt_size, ...) = (void *) 6; static int (*bpf_probe_read_user)(void *dst, __u32 size, const void *unsafe_ptr) = (void *) 112; static int (*bpf_probe_read_kernel)(void *dst, __u32 size, const void *unsafe_ptr) = (void *) 113; SEC("func=do_sched_setscheduler pid policy param->sched_priority@user") int bpf_func__setscheduler(void *ctx, int err, pid_t pid, int policy, int param) { char fmt[] = "prio: %ld"; bpf_trace_printk(fmt, sizeof(fmt), param); return 1; } char _license[] SEC("license") = "GPL"; int _version SEC("version") = LINUX_VERSION_CODE; 3. ./perf script sched 305669 [000] 1614458.838675: perf_bpf_probe:func: (2904e508) pid=261614 policy=2 sched_priority=1 4. cat /sys/kernel/debug/tracing/trace <...>-309956 [006] .... 1616098.093957: 0: prio: 1 Signed-off-by: Sumanth Korikkar <sumanthk@linux.ibm.com> Reviewed-by: Thomas Richter <tmricht@linux.ibm.com> --- tools/perf/util/bpf-prologue.c | 14 ++++++++++---- 1 file changed, 10 insertions(+), 4 deletions(-)