| Message ID | 6b6f14a32fc13e2f8de0f384cab5ae32ce5eb8e0.1602516273.git.andreyknvl@google.com (mailing list archive) |
|---|---|
| State | Superseded |
| Headers | show |
| Series | [v3] kcov, usb: specify contexts for remote coverage sections | expand |
On Mon, 12 Oct 2020 at 17:25, Andrey Konovalov <andreyknvl@google.com> wrote: > > Currently there's a KCOV remote coverage collection section in > __usb_hcd_giveback_urb(). Initially that section was added based on the > assumption that usb_hcd_giveback_urb() can only be called in interrupt > context as indicated by a comment before it. This is what happens when > syzkaller is fuzzing the USB stack via the dummy_hcd driver. > > As it turns out, it's actually valid to call usb_hcd_giveback_urb() in task > context, provided that the caller turned off the interrupts; USB/IP does > exactly that. This can lead to a nested KCOV remote coverage collection > sections both trying to collect coverage in task context. This isn't > supported by KCOV, and leads to a WARNING. > > The approach this patch takes is to add another set of kcov_remote_*() > callbacks that specify the context they are supposed to be executed in. > If the current context doesn't match the mask provided to a callback, > that callback is ignored. KCOV currently only supports collecting remote > coverage in two contexts: task and softirq. This patch constraints KCOV to > only collect coverage from __usb_hcd_giveback_urb() when it's executed in > softirq context. > > As the result, the coverage from USB/IP related usb_hcd_giveback_urb() calls > won't be collected, but the WARNING is fixed. > > A potential future improvement would be to support nested remote coverage > collection sections, but this patch doesn't address that. > > Signed-off-by: Andrey Konovalov <andreyknvl@google.com> > --- > > Changes v2->v3: > - Keep behavoir of existing callbacks the same except for the > __usb_hcd_giveback_urb() one. > - Fix build error with KOV disabled. > > --- > Documentation/dev-tools/kcov.rst | 6 ++++++ > drivers/usb/core/hcd.c | 4 ++-- > include/linux/kcov.h | 31 +++++++++++++++++++++++++++++-- > kernel/kcov.c | 26 +++++++++++++++++++------- > 4 files changed, 56 insertions(+), 11 deletions(-) > > diff --git a/Documentation/dev-tools/kcov.rst b/Documentation/dev-tools/kcov.rst > index 8548b0b04e43..2c0f58988512 100644 > --- a/Documentation/dev-tools/kcov.rst > +++ b/Documentation/dev-tools/kcov.rst > @@ -235,6 +235,12 @@ saved to the kcov_handle field in the current task_struct and needs to be > passed to the newly spawned threads via custom annotations. Those threads > should in turn be annotated with kcov_remote_start()/kcov_remote_stop(). > > +Besides the annotations that only accept a handle, there are also > +kcov_remote_start_context()/kcov_remote_stop_context() that accept a > +context mask. This mask describes the contexts in which these annotations > +should be applied. E.g. specifying KCOV_CONTEXT_SOFTIRQ will result in the > +corresponding annotations being ignored in any context other than softirq. > + > Internally kcov stores handles as u64 integers. The top byte of a handle > is used to denote the id of a subsystem that this handle belongs to, and > the lower 4 bytes are used to denote the id of a thread instance within > diff --git a/drivers/usb/core/hcd.c b/drivers/usb/core/hcd.c > index a33b849e8beb..ea93d9ebcb2e 100644 > --- a/drivers/usb/core/hcd.c > +++ b/drivers/usb/core/hcd.c > @@ -1646,9 +1646,9 @@ static void __usb_hcd_giveback_urb(struct urb *urb) > > /* pass ownership to the completion handler */ > urb->status = status; > - kcov_remote_start_usb((u64)urb->dev->bus->busnum); > + kcov_remote_start_usb_softirq((u64)urb->dev->bus->busnum); > urb->complete(urb); > - kcov_remote_stop(); > + kcov_remote_stop_softirq(); > > usb_anchor_resume_wakeups(anchor); > atomic_dec(&urb->use_count); > diff --git a/include/linux/kcov.h b/include/linux/kcov.h > index a10e84707d82..9e31b71ee3f9 100644 > --- a/include/linux/kcov.h > +++ b/include/linux/kcov.h > @@ -22,6 +22,10 @@ enum kcov_mode { > KCOV_MODE_TRACE_CMP = 3, > }; > > +#define KCOV_CONTEXT_TASK (1u << 0) > +#define KCOV_CONTEXT_SOFTIRQ (1u << 1) > +#define KCOV_CONTEXT_MASK (KCOV_CONTEXT_TASK | KCOV_CONTEXT_SOFTIRQ) > + > #define KCOV_IN_CTXSW (1 << 30) > > void kcov_task_init(struct task_struct *t); > @@ -38,10 +42,21 @@ do { \ > } while (0) > > /* See Documentation/dev-tools/kcov.rst for usage details. */ > -void kcov_remote_start(u64 handle); > -void kcov_remote_stop(void); > + > +void kcov_remote_start_context(u64 handle, unsigned int context); > +void kcov_remote_stop_context(unsigned int context); > u64 kcov_common_handle(void); > > +static inline void kcov_remote_start(u64 handle) > +{ > + return kcov_remote_start_context(handle, KCOV_CONTEXT_MASK); > +} > + > +static inline void kcov_remote_stop(void) > +{ > + return kcov_remote_stop_context(KCOV_CONTEXT_MASK); > +} These are returning void whereas kcov_remote_start_usb_softirq isn't. Was it intentional? Other than that, Acked-by: Marco Elver <elver@google.com> Thank you! > static inline void kcov_remote_start_common(u64 id) > { > kcov_remote_start(kcov_remote_handle(KCOV_SUBSYSTEM_COMMON, id)); > @@ -52,6 +67,16 @@ static inline void kcov_remote_start_usb(u64 id) > kcov_remote_start(kcov_remote_handle(KCOV_SUBSYSTEM_USB, id)); > } > > +static inline void kcov_remote_start_usb_softirq(u64 id) > +{ > + kcov_remote_start_context(kcov_remote_handle(KCOV_SUBSYSTEM_USB, id), KCOV_CONTEXT_SOFTIRQ); > +} > + > +static inline void kcov_remote_stop_softirq(void) > +{ > + return kcov_remote_stop_context(KCOV_CONTEXT_SOFTIRQ); > +} > + > #else > > static inline void kcov_task_init(struct task_struct *t) {} > @@ -66,6 +91,8 @@ static inline u64 kcov_common_handle(void) > } > static inline void kcov_remote_start_common(u64 id) {} > static inline void kcov_remote_start_usb(u64 id) {} > +static inline void kcov_remote_start_usb_softirq(u64 id) {} > +static inline void kcov_remote_stop_softirq(void) {} > > #endif /* CONFIG_KCOV */ > #endif /* _LINUX_KCOV_H */ > diff --git a/kernel/kcov.c b/kernel/kcov.c > index 6b8368be89c8..3ccdbe060f47 100644 > --- a/kernel/kcov.c > +++ b/kernel/kcov.c > @@ -808,7 +808,8 @@ static void kcov_remote_softirq_stop(struct task_struct *t) > } > } > > -void kcov_remote_start(u64 handle) > +/* Also see kcov_remote_start() defined in include/linux/kcov.h. */ > +void kcov_remote_start_context(u64 handle, unsigned int context) > { > struct task_struct *t = current; > struct kcov_remote *remote; > @@ -821,7 +822,11 @@ void kcov_remote_start(u64 handle) > > if (WARN_ON(!kcov_check_handle(handle, true, true, true))) > return; > - if (!in_task() && !in_serving_softirq()) > + if (WARN_ON((context & ~KCOV_CONTEXT_MASK) || !context)) > + return; > + if (in_task() && !(context & KCOV_CONTEXT_TASK)) > + return; > + if (in_serving_softirq() && !(context & KCOV_CONTEXT_SOFTIRQ)) > return; > > local_irq_save(flags); > @@ -894,7 +899,7 @@ void kcov_remote_start(u64 handle) > local_irq_restore(flags); > > } > -EXPORT_SYMBOL(kcov_remote_start); > +EXPORT_SYMBOL(kcov_remote_start_context); > > static void kcov_move_area(enum kcov_mode mode, void *dst_area, > unsigned int dst_area_size, void *src_area) > @@ -951,8 +956,11 @@ static void kcov_move_area(enum kcov_mode mode, void *dst_area, > } > } > > -/* See the comment before kcov_remote_start() for usage details. */ > -void kcov_remote_stop(void) > +/* > + * Also see kcov_remote_stop() defined in include/linux/kcov.h. > + * See the comment before kcov_remote_start_context() for usage details. > + */ > +void kcov_remote_stop_context(unsigned int context) > { > struct task_struct *t = current; > struct kcov *kcov; > @@ -962,7 +970,11 @@ void kcov_remote_stop(void) > int sequence; > unsigned long flags; > > - if (!in_task() && !in_serving_softirq()) > + if (WARN_ON((context & ~KCOV_CONTEXT_MASK) || !context)) > + return; > + if (in_task() && !(context & KCOV_CONTEXT_TASK)) > + return; > + if (in_serving_softirq() && !(context & KCOV_CONTEXT_SOFTIRQ)) > return; > > local_irq_save(flags); > @@ -1018,7 +1030,7 @@ void kcov_remote_stop(void) > /* Get in kcov_remote_start(). */ > kcov_put(kcov); > } > -EXPORT_SYMBOL(kcov_remote_stop); > +EXPORT_SYMBOL(kcov_remote_stop_context); > > /* See the comment before kcov_remote_start() for usage details. */ > u64 kcov_common_handle(void) > -- > 2.28.0.1011.ga647a8990f-goog >
On Mon, Oct 12, 2020 at 6:08 PM Marco Elver <elver@google.com> wrote: > > On Mon, 12 Oct 2020 at 17:25, Andrey Konovalov <andreyknvl@google.com> wrote: > > > > Currently there's a KCOV remote coverage collection section in > > __usb_hcd_giveback_urb(). Initially that section was added based on the > > assumption that usb_hcd_giveback_urb() can only be called in interrupt > > context as indicated by a comment before it. This is what happens when > > syzkaller is fuzzing the USB stack via the dummy_hcd driver. > > > > As it turns out, it's actually valid to call usb_hcd_giveback_urb() in task > > context, provided that the caller turned off the interrupts; USB/IP does > > exactly that. This can lead to a nested KCOV remote coverage collection > > sections both trying to collect coverage in task context. This isn't > > supported by KCOV, and leads to a WARNING. > > > > The approach this patch takes is to add another set of kcov_remote_*() > > callbacks that specify the context they are supposed to be executed in. > > If the current context doesn't match the mask provided to a callback, > > that callback is ignored. KCOV currently only supports collecting remote > > coverage in two contexts: task and softirq. This patch constraints KCOV to > > only collect coverage from __usb_hcd_giveback_urb() when it's executed in > > softirq context. > > > > As the result, the coverage from USB/IP related usb_hcd_giveback_urb() calls > > won't be collected, but the WARNING is fixed. > > > > A potential future improvement would be to support nested remote coverage > > collection sections, but this patch doesn't address that. > > > > Signed-off-by: Andrey Konovalov <andreyknvl@google.com> > > --- > > > > Changes v2->v3: > > - Keep behavoir of existing callbacks the same except for the > > __usb_hcd_giveback_urb() one. > > - Fix build error with KOV disabled. > > > > --- > > Documentation/dev-tools/kcov.rst | 6 ++++++ > > drivers/usb/core/hcd.c | 4 ++-- > > include/linux/kcov.h | 31 +++++++++++++++++++++++++++++-- > > kernel/kcov.c | 26 +++++++++++++++++++------- > > 4 files changed, 56 insertions(+), 11 deletions(-) > > > > diff --git a/Documentation/dev-tools/kcov.rst b/Documentation/dev-tools/kcov.rst > > index 8548b0b04e43..2c0f58988512 100644 > > --- a/Documentation/dev-tools/kcov.rst > > +++ b/Documentation/dev-tools/kcov.rst > > @@ -235,6 +235,12 @@ saved to the kcov_handle field in the current task_struct and needs to be > > passed to the newly spawned threads via custom annotations. Those threads > > should in turn be annotated with kcov_remote_start()/kcov_remote_stop(). > > > > +Besides the annotations that only accept a handle, there are also > > +kcov_remote_start_context()/kcov_remote_stop_context() that accept a > > +context mask. This mask describes the contexts in which these annotations > > +should be applied. E.g. specifying KCOV_CONTEXT_SOFTIRQ will result in the > > +corresponding annotations being ignored in any context other than softirq. > > + > > Internally kcov stores handles as u64 integers. The top byte of a handle > > is used to denote the id of a subsystem that this handle belongs to, and > > the lower 4 bytes are used to denote the id of a thread instance within > > diff --git a/drivers/usb/core/hcd.c b/drivers/usb/core/hcd.c > > index a33b849e8beb..ea93d9ebcb2e 100644 > > --- a/drivers/usb/core/hcd.c > > +++ b/drivers/usb/core/hcd.c > > @@ -1646,9 +1646,9 @@ static void __usb_hcd_giveback_urb(struct urb *urb) > > > > /* pass ownership to the completion handler */ > > urb->status = status; > > - kcov_remote_start_usb((u64)urb->dev->bus->busnum); > > + kcov_remote_start_usb_softirq((u64)urb->dev->bus->busnum); > > urb->complete(urb); > > - kcov_remote_stop(); > > + kcov_remote_stop_softirq(); > > > > usb_anchor_resume_wakeups(anchor); > > atomic_dec(&urb->use_count); > > diff --git a/include/linux/kcov.h b/include/linux/kcov.h > > index a10e84707d82..9e31b71ee3f9 100644 > > --- a/include/linux/kcov.h > > +++ b/include/linux/kcov.h > > @@ -22,6 +22,10 @@ enum kcov_mode { > > KCOV_MODE_TRACE_CMP = 3, > > }; > > > > +#define KCOV_CONTEXT_TASK (1u << 0) > > +#define KCOV_CONTEXT_SOFTIRQ (1u << 1) > > +#define KCOV_CONTEXT_MASK (KCOV_CONTEXT_TASK | KCOV_CONTEXT_SOFTIRQ) > > + > > #define KCOV_IN_CTXSW (1 << 30) > > > > void kcov_task_init(struct task_struct *t); > > @@ -38,10 +42,21 @@ do { \ > > } while (0) > > > > /* See Documentation/dev-tools/kcov.rst for usage details. */ > > -void kcov_remote_start(u64 handle); > > -void kcov_remote_stop(void); > > + > > +void kcov_remote_start_context(u64 handle, unsigned int context); > > +void kcov_remote_stop_context(unsigned int context); > > u64 kcov_common_handle(void); > > > > +static inline void kcov_remote_start(u64 handle) > > +{ > > + return kcov_remote_start_context(handle, KCOV_CONTEXT_MASK); > > +} > > + > > +static inline void kcov_remote_stop(void) > > +{ > > + return kcov_remote_stop_context(KCOV_CONTEXT_MASK); > > +} > > These are returning void whereas kcov_remote_start_usb_softirq isn't. > Was it intentional? Not intentional, thank you for noticing! Will fix in v4. > > Other than that, > > Acked-by: Marco Elver <elver@google.com> > > Thank you! Thanks! > > > static inline void kcov_remote_start_common(u64 id) > > { > > kcov_remote_start(kcov_remote_handle(KCOV_SUBSYSTEM_COMMON, id)); > > @@ -52,6 +67,16 @@ static inline void kcov_remote_start_usb(u64 id) > > kcov_remote_start(kcov_remote_handle(KCOV_SUBSYSTEM_USB, id)); > > } > > > > +static inline void kcov_remote_start_usb_softirq(u64 id) > > +{ > > + kcov_remote_start_context(kcov_remote_handle(KCOV_SUBSYSTEM_USB, id), KCOV_CONTEXT_SOFTIRQ); > > +} > > + > > +static inline void kcov_remote_stop_softirq(void) > > +{ > > + return kcov_remote_stop_context(KCOV_CONTEXT_SOFTIRQ); > > +} > > + > > #else > > > > static inline void kcov_task_init(struct task_struct *t) {} > > @@ -66,6 +91,8 @@ static inline u64 kcov_common_handle(void) > > } > > static inline void kcov_remote_start_common(u64 id) {} > > static inline void kcov_remote_start_usb(u64 id) {} > > +static inline void kcov_remote_start_usb_softirq(u64 id) {} > > +static inline void kcov_remote_stop_softirq(void) {} > > > > #endif /* CONFIG_KCOV */ > > #endif /* _LINUX_KCOV_H */ > > diff --git a/kernel/kcov.c b/kernel/kcov.c > > index 6b8368be89c8..3ccdbe060f47 100644 > > --- a/kernel/kcov.c > > +++ b/kernel/kcov.c > > @@ -808,7 +808,8 @@ static void kcov_remote_softirq_stop(struct task_struct *t) > > } > > } > > > > -void kcov_remote_start(u64 handle) > > +/* Also see kcov_remote_start() defined in include/linux/kcov.h. */ > > +void kcov_remote_start_context(u64 handle, unsigned int context) > > { > > struct task_struct *t = current; > > struct kcov_remote *remote; > > @@ -821,7 +822,11 @@ void kcov_remote_start(u64 handle) > > > > if (WARN_ON(!kcov_check_handle(handle, true, true, true))) > > return; > > - if (!in_task() && !in_serving_softirq()) > > + if (WARN_ON((context & ~KCOV_CONTEXT_MASK) || !context)) > > + return; > > + if (in_task() && !(context & KCOV_CONTEXT_TASK)) > > + return; > > + if (in_serving_softirq() && !(context & KCOV_CONTEXT_SOFTIRQ)) > > return; > > > > local_irq_save(flags); > > @@ -894,7 +899,7 @@ void kcov_remote_start(u64 handle) > > local_irq_restore(flags); > > > > } > > -EXPORT_SYMBOL(kcov_remote_start); > > +EXPORT_SYMBOL(kcov_remote_start_context); > > > > static void kcov_move_area(enum kcov_mode mode, void *dst_area, > > unsigned int dst_area_size, void *src_area) > > @@ -951,8 +956,11 @@ static void kcov_move_area(enum kcov_mode mode, void *dst_area, > > } > > } > > > > -/* See the comment before kcov_remote_start() for usage details. */ > > -void kcov_remote_stop(void) > > +/* > > + * Also see kcov_remote_stop() defined in include/linux/kcov.h. > > + * See the comment before kcov_remote_start_context() for usage details. > > + */ > > +void kcov_remote_stop_context(unsigned int context) > > { > > struct task_struct *t = current; > > struct kcov *kcov; > > @@ -962,7 +970,11 @@ void kcov_remote_stop(void) > > int sequence; > > unsigned long flags; > > > > - if (!in_task() && !in_serving_softirq()) > > + if (WARN_ON((context & ~KCOV_CONTEXT_MASK) || !context)) > > + return; > > + if (in_task() && !(context & KCOV_CONTEXT_TASK)) > > + return; > > + if (in_serving_softirq() && !(context & KCOV_CONTEXT_SOFTIRQ)) > > return; > > > > local_irq_save(flags); > > @@ -1018,7 +1030,7 @@ void kcov_remote_stop(void) > > /* Get in kcov_remote_start(). */ > > kcov_put(kcov); > > } > > -EXPORT_SYMBOL(kcov_remote_stop); > > +EXPORT_SYMBOL(kcov_remote_stop_context); > > > > /* See the comment before kcov_remote_start() for usage details. */ > > u64 kcov_common_handle(void) > > -- > > 2.28.0.1011.ga647a8990f-goog > >
diff --git a/Documentation/dev-tools/kcov.rst b/Documentation/dev-tools/kcov.rst index 8548b0b04e43..2c0f58988512 100644 --- a/Documentation/dev-tools/kcov.rst +++ b/Documentation/dev-tools/kcov.rst @@ -235,6 +235,12 @@ saved to the kcov_handle field in the current task_struct and needs to be passed to the newly spawned threads via custom annotations. Those threads should in turn be annotated with kcov_remote_start()/kcov_remote_stop(). +Besides the annotations that only accept a handle, there are also +kcov_remote_start_context()/kcov_remote_stop_context() that accept a +context mask. This mask describes the contexts in which these annotations +should be applied. E.g. specifying KCOV_CONTEXT_SOFTIRQ will result in the +corresponding annotations being ignored in any context other than softirq. + Internally kcov stores handles as u64 integers. The top byte of a handle is used to denote the id of a subsystem that this handle belongs to, and the lower 4 bytes are used to denote the id of a thread instance within diff --git a/drivers/usb/core/hcd.c b/drivers/usb/core/hcd.c index a33b849e8beb..ea93d9ebcb2e 100644 --- a/drivers/usb/core/hcd.c +++ b/drivers/usb/core/hcd.c @@ -1646,9 +1646,9 @@ static void __usb_hcd_giveback_urb(struct urb *urb) /* pass ownership to the completion handler */ urb->status = status; - kcov_remote_start_usb((u64)urb->dev->bus->busnum); + kcov_remote_start_usb_softirq((u64)urb->dev->bus->busnum); urb->complete(urb); - kcov_remote_stop(); + kcov_remote_stop_softirq(); usb_anchor_resume_wakeups(anchor); atomic_dec(&urb->use_count); diff --git a/include/linux/kcov.h b/include/linux/kcov.h index a10e84707d82..9e31b71ee3f9 100644 --- a/include/linux/kcov.h +++ b/include/linux/kcov.h @@ -22,6 +22,10 @@ enum kcov_mode { KCOV_MODE_TRACE_CMP = 3, }; +#define KCOV_CONTEXT_TASK (1u << 0) +#define KCOV_CONTEXT_SOFTIRQ (1u << 1) +#define KCOV_CONTEXT_MASK (KCOV_CONTEXT_TASK | KCOV_CONTEXT_SOFTIRQ) + #define KCOV_IN_CTXSW (1 << 30) void kcov_task_init(struct task_struct *t); @@ -38,10 +42,21 @@ do { \ } while (0) /* See Documentation/dev-tools/kcov.rst for usage details. */ -void kcov_remote_start(u64 handle); -void kcov_remote_stop(void); + +void kcov_remote_start_context(u64 handle, unsigned int context); +void kcov_remote_stop_context(unsigned int context); u64 kcov_common_handle(void); +static inline void kcov_remote_start(u64 handle) +{ + return kcov_remote_start_context(handle, KCOV_CONTEXT_MASK); +} + +static inline void kcov_remote_stop(void) +{ + return kcov_remote_stop_context(KCOV_CONTEXT_MASK); +} + static inline void kcov_remote_start_common(u64 id) { kcov_remote_start(kcov_remote_handle(KCOV_SUBSYSTEM_COMMON, id)); @@ -52,6 +67,16 @@ static inline void kcov_remote_start_usb(u64 id) kcov_remote_start(kcov_remote_handle(KCOV_SUBSYSTEM_USB, id)); } +static inline void kcov_remote_start_usb_softirq(u64 id) +{ + kcov_remote_start_context(kcov_remote_handle(KCOV_SUBSYSTEM_USB, id), KCOV_CONTEXT_SOFTIRQ); +} + +static inline void kcov_remote_stop_softirq(void) +{ + return kcov_remote_stop_context(KCOV_CONTEXT_SOFTIRQ); +} + #else static inline void kcov_task_init(struct task_struct *t) {} @@ -66,6 +91,8 @@ static inline u64 kcov_common_handle(void) } static inline void kcov_remote_start_common(u64 id) {} static inline void kcov_remote_start_usb(u64 id) {} +static inline void kcov_remote_start_usb_softirq(u64 id) {} +static inline void kcov_remote_stop_softirq(void) {} #endif /* CONFIG_KCOV */ #endif /* _LINUX_KCOV_H */ diff --git a/kernel/kcov.c b/kernel/kcov.c index 6b8368be89c8..3ccdbe060f47 100644 --- a/kernel/kcov.c +++ b/kernel/kcov.c @@ -808,7 +808,8 @@ static void kcov_remote_softirq_stop(struct task_struct *t) } } -void kcov_remote_start(u64 handle) +/* Also see kcov_remote_start() defined in include/linux/kcov.h. */ +void kcov_remote_start_context(u64 handle, unsigned int context) { struct task_struct *t = current; struct kcov_remote *remote; @@ -821,7 +822,11 @@ void kcov_remote_start(u64 handle) if (WARN_ON(!kcov_check_handle(handle, true, true, true))) return; - if (!in_task() && !in_serving_softirq()) + if (WARN_ON((context & ~KCOV_CONTEXT_MASK) || !context)) + return; + if (in_task() && !(context & KCOV_CONTEXT_TASK)) + return; + if (in_serving_softirq() && !(context & KCOV_CONTEXT_SOFTIRQ)) return; local_irq_save(flags); @@ -894,7 +899,7 @@ void kcov_remote_start(u64 handle) local_irq_restore(flags); } -EXPORT_SYMBOL(kcov_remote_start); +EXPORT_SYMBOL(kcov_remote_start_context); static void kcov_move_area(enum kcov_mode mode, void *dst_area, unsigned int dst_area_size, void *src_area) @@ -951,8 +956,11 @@ static void kcov_move_area(enum kcov_mode mode, void *dst_area, } } -/* See the comment before kcov_remote_start() for usage details. */ -void kcov_remote_stop(void) +/* + * Also see kcov_remote_stop() defined in include/linux/kcov.h. + * See the comment before kcov_remote_start_context() for usage details. + */ +void kcov_remote_stop_context(unsigned int context) { struct task_struct *t = current; struct kcov *kcov; @@ -962,7 +970,11 @@ void kcov_remote_stop(void) int sequence; unsigned long flags; - if (!in_task() && !in_serving_softirq()) + if (WARN_ON((context & ~KCOV_CONTEXT_MASK) || !context)) + return; + if (in_task() && !(context & KCOV_CONTEXT_TASK)) + return; + if (in_serving_softirq() && !(context & KCOV_CONTEXT_SOFTIRQ)) return; local_irq_save(flags); @@ -1018,7 +1030,7 @@ void kcov_remote_stop(void) /* Get in kcov_remote_start(). */ kcov_put(kcov); } -EXPORT_SYMBOL(kcov_remote_stop); +EXPORT_SYMBOL(kcov_remote_stop_context); /* See the comment before kcov_remote_start() for usage details. */ u64 kcov_common_handle(void)
Currently there's a KCOV remote coverage collection section in __usb_hcd_giveback_urb(). Initially that section was added based on the assumption that usb_hcd_giveback_urb() can only be called in interrupt context as indicated by a comment before it. This is what happens when syzkaller is fuzzing the USB stack via the dummy_hcd driver. As it turns out, it's actually valid to call usb_hcd_giveback_urb() in task context, provided that the caller turned off the interrupts; USB/IP does exactly that. This can lead to a nested KCOV remote coverage collection sections both trying to collect coverage in task context. This isn't supported by KCOV, and leads to a WARNING. The approach this patch takes is to add another set of kcov_remote_*() callbacks that specify the context they are supposed to be executed in. If the current context doesn't match the mask provided to a callback, that callback is ignored. KCOV currently only supports collecting remote coverage in two contexts: task and softirq. This patch constraints KCOV to only collect coverage from __usb_hcd_giveback_urb() when it's executed in softirq context. As the result, the coverage from USB/IP related usb_hcd_giveback_urb() calls won't be collected, but the WARNING is fixed. A potential future improvement would be to support nested remote coverage collection sections, but this patch doesn't address that. Signed-off-by: Andrey Konovalov <andreyknvl@google.com> --- Changes v2->v3: - Keep behavoir of existing callbacks the same except for the __usb_hcd_giveback_urb() one. - Fix build error with KOV disabled. --- Documentation/dev-tools/kcov.rst | 6 ++++++ drivers/usb/core/hcd.c | 4 ++-- include/linux/kcov.h | 31 +++++++++++++++++++++++++++++-- kernel/kcov.c | 26 +++++++++++++++++++------- 4 files changed, 56 insertions(+), 11 deletions(-)