diff mbox series

[bpf-next,v2,4/4] ftrace: Fix dead loop caused by direct call in ftrace selftest

Message ID 20220913162732.163631-5-xukuohai@huaweicloud.com (mailing list archive)
State Awaiting Upstream
Delegated to: BPF
Headers show
Series Add ftrace direct call for arm64 | expand

Checks

Context Check Description
netdev/tree_selection success Clearly marked for bpf-next
netdev/fixes_present success Fixes tag not required for -next series
netdev/subject_prefix success Link
netdev/cover_letter success Series has a cover letter
netdev/patch_count success Link
netdev/header_inline success No static functions without inline keyword in header files
netdev/build_32bit success Errors and warnings before: 10 this patch: 10
netdev/cc_maintainers success CCed 6 of 6 maintainers
netdev/build_clang success Errors and warnings before: 5 this patch: 5
netdev/module_param success Was 0 now: 0
netdev/verify_signedoff success Signed-off-by tag matches author and committer
netdev/check_selftest success No net selftest shell script
netdev/verify_fixes success No Fixes tag
netdev/build_allmodconfig_warn success Errors and warnings before: 10 this patch: 10
netdev/checkpatch success total: 0 errors, 0 warnings, 0 checks, 20 lines checked
netdev/kdoc success Errors and warnings before: 0 this patch: 0
netdev/source_inline success Was 0 now: 0
bpf/vmtest-bpf-next-PR fail PR summary
bpf/vmtest-bpf-next-VM_Test-15 success Logs for test_verifier on s390x with gcc
bpf/vmtest-bpf-next-VM_Test-9 success Logs for test_progs on s390x with gcc
bpf/vmtest-bpf-next-VM_Test-12 fail Logs for test_progs_no_alu32 on s390x with gcc
bpf/vmtest-bpf-next-VM_Test-6 success Logs for test_maps on s390x with gcc
bpf/vmtest-bpf-next-VM_Test-4 success Logs for llvm-toolchain
bpf/vmtest-bpf-next-VM_Test-5 success Logs for set-matrix
bpf/vmtest-bpf-next-VM_Test-2 success Logs for build for x86_64 with gcc
bpf/vmtest-bpf-next-VM_Test-3 success Logs for build for x86_64 with llvm-16
bpf/vmtest-bpf-next-VM_Test-1 success Logs for build for s390x with gcc
bpf/vmtest-bpf-next-VM_Test-16 success Logs for test_verifier on x86_64 with gcc
bpf/vmtest-bpf-next-VM_Test-17 success Logs for test_verifier on x86_64 with llvm-16
bpf/vmtest-bpf-next-VM_Test-10 success Logs for test_progs on x86_64 with gcc
bpf/vmtest-bpf-next-VM_Test-13 success Logs for test_progs_no_alu32 on x86_64 with gcc
bpf/vmtest-bpf-next-VM_Test-14 success Logs for test_progs_no_alu32 on x86_64 with llvm-16
bpf/vmtest-bpf-next-VM_Test-11 success Logs for test_progs on x86_64 with llvm-16
bpf/vmtest-bpf-next-VM_Test-7 success Logs for test_maps on x86_64 with gcc
bpf/vmtest-bpf-next-VM_Test-8 success Logs for test_maps on x86_64 with llvm-16

Commit Message

Xu Kuohai Sept. 13, 2022, 4:27 p.m. UTC 
From: Xu Kuohai <xukuohai@huawei.com>

After direct call is enabled for arm64, ftrace selftest enters a
dead loop:

<trace_selftest_dynamic_test_func>:
00  bti     c
01  mov     x9, x30                            <trace_direct_tramp>:
02  bl      <trace_direct_tramp>    ---------->     ret
                                                     |
                                         lr/x30 is 03, return to 03
                                                     |
03  mov     w0, #0x0   <-----------------------------|
     |                                               |
     |                   dead loop!                  |
     |                                               |
04  ret   ---- lr/x30 is still 03, go back to 03 ----|

The reason is that when the direct caller trace_direct_tramp() returns
to the patched function trace_selftest_dynamic_test_func(), lr is still
the address after the instrumented instruction in the patched function,
so when the patched function exits, it returns to itself!

To fix this issue, we need to restore lr before trace_direct_tramp()
exits, so use a dedicated trace_direct_tramp() for arm64.

Reported-by: Li Huafei <lihuafei1@huawei.com>
Signed-off-by: Xu Kuohai <xukuohai@huawei.com>
Acked-by: Steven Rostedt (Google) <rostedt@goodmis.org>
---
 arch/arm64/include/asm/ftrace.h | 4 ++++
 kernel/trace/trace_selftest.c   | 2 ++
 2 files changed, 6 insertions(+)
diff mbox series

Patch

diff --git a/arch/arm64/include/asm/ftrace.h b/arch/arm64/include/asm/ftrace.h
index b07a3c24f918..15247f73bf54 100644
--- a/arch/arm64/include/asm/ftrace.h
+++ b/arch/arm64/include/asm/ftrace.h
@@ -128,6 +128,10 @@  static inline bool arch_syscall_match_sym_name(const char *sym,
 #define ftrace_dummy_tramp ftrace_dummy_tramp
 extern void ftrace_dummy_tramp(void);
 
+#ifdef CONFIG_FTRACE_SELFTEST
+#define trace_direct_tramp ftrace_dummy_tramp
+#endif /* CONFIG_FTRACE_SELFTEST */
+
 #endif /* CONFIG_DYNAMIC_FTRACE_WITH_DIRECT_CALLS */
 
 #endif /* ifndef __ASSEMBLY__ */
diff --git a/kernel/trace/trace_selftest.c b/kernel/trace/trace_selftest.c
index a2d301f58ced..092239bc373c 100644
--- a/kernel/trace/trace_selftest.c
+++ b/kernel/trace/trace_selftest.c
@@ -785,8 +785,10 @@  static struct fgraph_ops fgraph_ops __initdata  = {
 };
 
 #ifdef CONFIG_DYNAMIC_FTRACE_WITH_DIRECT_CALLS
+#ifndef trace_direct_tramp
 noinline __noclone static void trace_direct_tramp(void) { }
 #endif
+#endif
 
 /*
  * Pretty much the same than for the function tracer from which the selftest