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Wed, 18 Mar 2026 09:27:11 -0700 (PDT) From: Jann Horn Date: Wed, 18 Mar 2026 17:27:00 +0100 Subject: [PATCH v2 3/4] kcov: refactor mode check out of check_kcov_mode() Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable Message-Id: <20260318-kcov-extrecord-v2-3-2522da6fcd3f@google.com> References: <20260318-kcov-extrecord-v2-0-2522da6fcd3f@google.com> In-Reply-To: <20260318-kcov-extrecord-v2-0-2522da6fcd3f@google.com> To: Dmitry Vyukov , Andrey Konovalov , Alexander Potapenko Cc: Nathan Chancellor , Nick Desaulniers , Bill Wendling , Justin Stitt , linux-kernel@vger.kernel.org, kasan-dev@googlegroups.com, llvm@lists.linux.dev, Jann Horn X-Mailer: b4 0.15-dev X-Developer-Signature: v=1; a=ed25519-sha256; t=1773851224; l=4314; i=jannh@google.com; s=20240730; h=from:subject:message-id; bh=GMMooYTgIpzRxthzUDxwLp4xKLUvtXfQIrOtNj3xG6o=; b=ubeizWU7XosiwCUKAEAZUXL1Q5MjoVYWTgMWVezx+AP3JNdQUC7UZ2ZhqtSoXWoWtZVUY+Iq1 IX5YDd6rFdVAEaAA4kXAvWENoyBRDOrwWqpuLocf+KNg0Hfew97r04r X-Developer-Key: i=jannh@google.com; a=ed25519; pk=AljNtGOzXeF6khBXDJVVvwSEkVDGnnZZYqfWhP1V+C8= The following patch will need to check t->kcov_mode in different ways at different check_kcov_mode() call sites. In preparation for that, move the mode check up the call hierarchy. Signed-off-by: Jann Horn --- kernel/kcov.c | 31 +++++++++++++++++-------------- 1 file changed, 17 insertions(+), 14 deletions(-) diff --git a/kernel/kcov.c b/kernel/kcov.c index 86b681c7865c..7edb39e18bfe 100644 --- a/kernel/kcov.c +++ b/kernel/kcov.c @@ -171,10 +171,8 @@ static __always_inline bool in_softirq_really(void) return in_serving_softirq() && !in_hardirq() && !in_nmi(); } =20 -static notrace bool check_kcov_mode(enum kcov_mode needed_mode, struct tas= k_struct *t) +static notrace bool check_kcov_context(struct task_struct *t) { - unsigned int mode; - /* * We are interested in code coverage as a function of a syscall inputs, * so we ignore code executed in interrupts, unless we are in a remote @@ -182,7 +180,6 @@ static notrace bool check_kcov_mode(enum kcov_mode need= ed_mode, struct task_stru */ if (!in_task() && !(in_softirq_really() && t->kcov_softirq)) return false; - mode =3D READ_ONCE(t->kcov_mode); /* * There is some code that runs in interrupts but for which * in_interrupt() returns false (e.g. preempt_schedule_irq()). @@ -191,7 +188,7 @@ static notrace bool check_kcov_mode(enum kcov_mode need= ed_mode, struct task_stru * kcov_start(). */ barrier(); - return mode =3D=3D needed_mode; + return true; } =20 static notrace unsigned long canonicalize_ip(unsigned long ip) @@ -202,14 +199,12 @@ static notrace unsigned long canonicalize_ip(unsigned= long ip) return ip; } =20 -static __always_inline void notrace kcov_add_pc_record(unsigned long recor= d) +static __always_inline void notrace kcov_add_pc_record(struct task_struct = *t, unsigned long record) { - struct task_struct *t; unsigned long *area; unsigned long pos; =20 - t =3D current; - if (!check_kcov_mode(KCOV_MODE_TRACE_PC, t)) + if (!check_kcov_context(t)) return; =20 area =3D t->kcov_area; @@ -217,7 +212,7 @@ static __always_inline void notrace kcov_add_pc_record(= unsigned long record) pos =3D READ_ONCE(area[0]) + 1; if (likely(pos < t->kcov_size)) { /* Previously we write pc before updating pos. However, some - * early interrupt code could bypass check_kcov_mode() check + * early interrupt code could bypass check_kcov_context() check * and invoke __sanitizer_cov_trace_pc(). If such interrupt is * raised between writing pc and updating pos, the pc could be * overitten by the recursive __sanitizer_cov_trace_pc(). @@ -235,20 +230,28 @@ static __always_inline void notrace kcov_add_pc_recor= d(unsigned long record) */ void notrace __sanitizer_cov_trace_pc(void) { - kcov_add_pc_record(canonicalize_ip(_RET_IP_)); + struct task_struct *cur =3D current; + + if (READ_ONCE(cur->kcov_mode) !=3D KCOV_MODE_TRACE_PC) + return; + kcov_add_pc_record(cur, canonicalize_ip(_RET_IP_)); } EXPORT_SYMBOL(__sanitizer_cov_trace_pc); =20 #ifdef CONFIG_KCOV_EXT_RECORDS void notrace __sanitizer_cov_trace_pc_entry(void) { + struct task_struct *cur =3D current; unsigned long record =3D canonicalize_ip(_RET_IP_); + unsigned int kcov_mode =3D READ_ONCE(cur->kcov_mode); =20 /* * This hook replaces __sanitizer_cov_trace_pc() for the function entry * basic block; it should still emit a record even in classic kcov mode. */ - kcov_add_pc_record(record); + if (kcov_mode !=3D KCOV_MODE_TRACE_PC) + return; + kcov_add_pc_record(cur, record); } void notrace __sanitizer_cov_trace_pc_exit(void) { @@ -263,7 +266,7 @@ static void notrace write_comp_data(u64 type, u64 arg1,= u64 arg2, u64 ip) u64 count, start_index, end_pos, max_pos; =20 t =3D current; - if (!check_kcov_mode(KCOV_MODE_TRACE_CMP, t)) + if (READ_ONCE(t->kcov_mode) !=3D KCOV_MODE_TRACE_CMP || !check_kcov_conte= xt(t)) return; =20 ip =3D canonicalize_ip(ip); @@ -383,7 +386,7 @@ static void kcov_start(struct task_struct *t, struct kc= ov *kcov, t->kcov_size =3D size; t->kcov_area =3D area; t->kcov_sequence =3D sequence; - /* See comment in check_kcov_mode(). */ + /* See comment in check_kcov_context(). */ barrier(); WRITE_ONCE(t->kcov_mode, mode); } --=20 2.53.0.851.ga537e3e6e9-goog