diff mbox series

[bpf-next,v2,22/31] libbpf: Fix unbounded memory access in bpf_usdt_arg()

Message ID 20230128000650.1516334-23-iii@linux.ibm.com (mailing list archive)
State Superseded
Commit 25c76ed428219127aba385d40756f6d5814e96e9
Delegated to: BPF
Headers show
Series Support bpf trampoline for s390x | expand

Checks

Context Check Description
netdev/tree_selection success Clearly marked for bpf-next, async
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 fail Series longer than 15 patches (and no cover letter)
netdev/header_inline success No static functions without inline keyword in header files
netdev/build_32bit success Errors and warnings before: 0 this patch: 0
netdev/cc_maintainers warning 8 maintainers not CCed: sdf@google.com kpsingh@kernel.org jolsa@kernel.org martin.lau@linux.dev song@kernel.org john.fastabend@gmail.com haoluo@google.com yhs@fb.com
netdev/build_clang success Errors and warnings before: 0 this patch: 0
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: 0 this patch: 0
netdev/checkpatch success total: 0 errors, 0 warnings, 0 checks, 11 lines checked
netdev/kdoc success Errors and warnings before: 0 this patch: 0
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Commit Message

Ilya Leoshkevich Jan. 28, 2023, 12:06 a.m. UTC 
Loading programs that use bpf_usdt_arg() on s390x fails with:

    ; if (arg_num >= BPF_USDT_MAX_ARG_CNT || arg_num >= spec->arg_cnt)
    128: (79) r1 = *(u64 *)(r10 -24)      ; frame1: R1_w=scalar(umax=4294967295,var_off=(0x0; 0xffffffff)) R10=fp0
    129: (25) if r1 > 0xb goto pc+83      ; frame1: R1_w=scalar(umax=11,var_off=(0x0; 0xf))
    ...
    ; arg_spec = &spec->args[arg_num];
    135: (79) r1 = *(u64 *)(r10 -24)      ; frame1: R1_w=scalar(umax=4294967295,var_off=(0x0; 0xffffffff)) R10=fp0
    ...
    ; switch (arg_spec->arg_type) {
    139: (61) r1 = *(u32 *)(r2 +8)
    R2 unbounded memory access, make sure to bounds check any such access

The reason is that, even though the C code enforces that
arg_num < BPF_USDT_MAX_ARG_CNT, the verifier cannot propagate this
constraint to the arg_spec assignment yet. Help it by forcing r1 back
to stack after comparison.

Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
---
 tools/lib/bpf/usdt.bpf.h | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)
diff mbox series

Patch

diff --git a/tools/lib/bpf/usdt.bpf.h b/tools/lib/bpf/usdt.bpf.h
index fdfd235e52c4..0bd4c135acc2 100644
--- a/tools/lib/bpf/usdt.bpf.h
+++ b/tools/lib/bpf/usdt.bpf.h
@@ -130,7 +130,10 @@  int bpf_usdt_arg(struct pt_regs *ctx, __u64 arg_num, long *res)
 	if (!spec)
 		return -ESRCH;
 
-	if (arg_num >= BPF_USDT_MAX_ARG_CNT || arg_num >= spec->arg_cnt)
+	if (arg_num >= BPF_USDT_MAX_ARG_CNT)
+		return -ENOENT;
+	barrier_var(arg_num);
+	if (arg_num >= spec->arg_cnt)
 		return -ENOENT;
 
 	arg_spec = &spec->args[arg_num];