fix(driver/modern_bpf): read signal_deliver siginfo via BPF_CORE_READ - #3119
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Signal tracepoints can receive the `SEND_SIG_NOINFO` (0) and
`SEND_SIG_PRIV` (1) sentinels in place of a real `kernel_siginfo`
pointer. Since `SEND_SIG_PRIV` survives a NULL check, kernel commit
77515ab12e49 ("bpf: Mark signal tracepoint siginfo arguments as
scalar") lists `signal_generate` and `signal_deliver` in
`raw_tp_null_args[]` and exposes the `info` argument to `tp_btf`
programs as a scalar.
With that change the verifier rejects the direct `info->...` accesses
in the `signal_deliver` program with "invalid mem access 'scalar'",
and since all programs are loaded together the modern probe fails to
load entirely (seen on 6.18.53).
Read the fields through `BPF_CORE_READ` instead. It is accepted both
when `info` is a scalar and when it is a BTF pointer, so older
kernels keep working. The resulting `spid` values are unchanged.
Link: torvalds/linux@77515ab
Signed-off-by: Adnan Ali <adduali1310@hotmail.com>
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Signal tracepoints can receive the
SEND_SIG_NOINFO(0) andSEND_SIG_PRIV(1) sentinels in place of a realkernel_siginfopointer. SinceSEND_SIG_PRIVsurvives a NULL check, kernel commit 77515ab12e49 ("bpf: Mark signal tracepoint siginfo arguments as scalar") listssignal_generateandsignal_deliverinraw_tp_null_args[]and exposes theinfoargument totp_btfprograms as a scalar.With that change the verifier rejects the direct
info->...accesses in thesignal_deliverprogram with "invalid mem access 'scalar'", and since all programs are loaded together the modern probe fails to load entirely (seen on 6.18.53).Read the fields through
BPF_CORE_READinstead. It is accepted both wheninfois a scalar and when it is a BTF pointer, so older kernels keep working. The resultingspidvalues are unchanged.Link: torvalds/linux@77515ab
What type of PR is this?
/kind bug
Any specific area of the project related to this PR?
/area driver-modern-bpf
What this PR does / why we need it:
Newer kernels add
signal_generateandsignal_delivertoraw_tp_null_args[]and expose theirinfoargument totp_btfprograms as a scalar, because it can be theSEND_SIG_PRIV(1) sentinel rather than a realpointer. The verifier then rejects the direct
info->...dereferences in oursignal_deliverprogram (invalid mem access 'scalar') and the whole modern probe fails to load (seen on 6.18.53).This switches those reads to
BPF_CORE_READ, which the verifier accepts for both the scalar and the BTF pointer case, so older kernels are unaffected. The kmod is not affected.Kernel commit: 77515ab12e49 ("bpf: Mark signal tracepoint siginfo arguments as scalar")
Which issue(s) this PR fixes:
Fixes #3118
Special notes for your reviewer:
Does this PR introduce a user-facing change?:
No