| Message ID | 20241030-kprobes-fix-counted-by-annotation-v1-1-8f266001fad0@kernel.org (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | kprobes: Adjustments for __counted_by addition | expand |
On Wed, 30 Oct 2024 09:14:48 -0700 Nathan Chancellor <nathan@kernel.org> wrote: > Commit 0888460c9050 ("kprobes: Annotate structs with __counted_by()") > added a __counted_by annotation without adjusting the code for the > __counted_by requirements, resulting in a panic when UBSAN_BOUNDS and > FORTIFY_SOURCE are enabled: > > | memset: detected buffer overflow: 512 byte write of buffer size 0 > | WARNING: CPU: 0 PID: 1 at lib/string_helpers.c:1032 __fortify_report+0x64/0x80 > | Call Trace: > | __fortify_report+0x60/0x80 (unreliable) > | __fortify_panic+0x18/0x1c > | __get_insn_slot+0x33c/0x340 > > __counted_by requires that the counter be set before accessing the > flexible array but ->nused is not set until after ->slot_used is > accessed via memset(). Even if the current ->nused assignment were moved > up before memset(), the value of 1 would be incorrect because the entire > array is being accessed, not just one element. Ah, I think I misunderstood the __counted_by(). If so, ->nused can be smaller than the accessing element of slot_used[]. I should revert it. The accessing index and ->nused should have no relationship. for example, slots_per_page(c) is 10, and 10 kprobes are registered and then, the 1st and 2nd kprobes are unregistered. At this moment, ->nused is 8 but slot_used[9] is still used. To unregister this 10th kprobe, we have to access slot_used[9]. So let's just revert the commit 0888460c9050. Thank you, > > Set ->nused to the full number of slots from slots_per_page() before > calling memset() to resolve the panic. While it is not strictly > necessary because of the new assignment, move the existing ->nused > assignment above accessing ->slot_used[0] for visual consistency. > > The value of slots_per_page() should not change throughout > __get_insn_slot() because ->insn_size is never modified after its > initial assignment (which has to be done by this point otherwise it > would be incorrect) and the other values are constants, so use a new > variable to reuse its value directly. > > Fixes: 0888460c9050 ("kprobes: Annotate structs with __counted_by()") > Signed-off-by: Nathan Chancellor <nathan@kernel.org> > --- > kernel/kprobes.c | 16 ++++++++++------ > 1 file changed, 10 insertions(+), 6 deletions(-) > > diff --git a/kernel/kprobes.c b/kernel/kprobes.c > index 98d71a5acb723ddfff3efcc44cc6754ee36ec1de..2cf4628bc97ce2ae18547b513cd75b6350e9cc9c 100644 > --- a/kernel/kprobes.c > +++ b/kernel/kprobes.c > @@ -145,16 +145,18 @@ kprobe_opcode_t *__get_insn_slot(struct kprobe_insn_cache *c) > { > struct kprobe_insn_page *kip; > kprobe_opcode_t *slot = NULL; > + int num_slots; > > /* Since the slot array is not protected by rcu, we need a mutex */ > mutex_lock(&c->mutex); > + num_slots = slots_per_page(c); > retry: > rcu_read_lock(); > list_for_each_entry_rcu(kip, &c->pages, list) { > - if (kip->nused < slots_per_page(c)) { > + if (kip->nused < num_slots) { > int i; > > - for (i = 0; i < slots_per_page(c); i++) { > + for (i = 0; i < num_slots; i++) { > if (kip->slot_used[i] == SLOT_CLEAN) { > kip->slot_used[i] = SLOT_USED; > kip->nused++; > @@ -164,7 +166,7 @@ kprobe_opcode_t *__get_insn_slot(struct kprobe_insn_cache *c) > } > } > /* kip->nused is broken. Fix it. */ > - kip->nused = slots_per_page(c); > + kip->nused = num_slots; > WARN_ON(1); > } > } > @@ -175,7 +177,7 @@ kprobe_opcode_t *__get_insn_slot(struct kprobe_insn_cache *c) > goto retry; > > /* All out of space. Need to allocate a new page. */ > - kip = kmalloc(KPROBE_INSN_PAGE_SIZE(slots_per_page(c)), GFP_KERNEL); > + kip = kmalloc(KPROBE_INSN_PAGE_SIZE(num_slots), GFP_KERNEL); > if (!kip) > goto out; > > @@ -185,9 +187,11 @@ kprobe_opcode_t *__get_insn_slot(struct kprobe_insn_cache *c) > goto out; > } > INIT_LIST_HEAD(&kip->list); > - memset(kip->slot_used, SLOT_CLEAN, slots_per_page(c)); > - kip->slot_used[0] = SLOT_USED; > + /* nused must be set before accessing slot_used */ > + kip->nused = num_slots; > + memset(kip->slot_used, SLOT_CLEAN, num_slots); > kip->nused = 1; > + kip->slot_used[0] = SLOT_USED; > kip->ngarbage = 0; > kip->cache = c; > list_add_rcu(&kip->list, &c->pages); > > -- > 2.47.0 >
On Thu, Oct 31, 2024 at 10:58:27AM +0900, Masami Hiramatsu wrote: > On Wed, 30 Oct 2024 09:14:48 -0700 > Nathan Chancellor <nathan@kernel.org> wrote: > > > Commit 0888460c9050 ("kprobes: Annotate structs with __counted_by()") > > added a __counted_by annotation without adjusting the code for the > > __counted_by requirements, resulting in a panic when UBSAN_BOUNDS and > > FORTIFY_SOURCE are enabled: > > > > | memset: detected buffer overflow: 512 byte write of buffer size 0 > > | WARNING: CPU: 0 PID: 1 at lib/string_helpers.c:1032 __fortify_report+0x64/0x80 > > | Call Trace: > > | __fortify_report+0x60/0x80 (unreliable) > > | __fortify_panic+0x18/0x1c > > | __get_insn_slot+0x33c/0x340 > > > > __counted_by requires that the counter be set before accessing the > > flexible array but ->nused is not set until after ->slot_used is > > accessed via memset(). Even if the current ->nused assignment were moved > > up before memset(), the value of 1 would be incorrect because the entire > > array is being accessed, not just one element. > > Ah, I think I misunderstood the __counted_by(). If so, ->nused can be > smaller than the accessing element of slot_used[]. I should revert it. > The accessing index and ->nused should have no relationship. > > for example, slots_per_page(c) is 10, and 10 kprobes are registered > and then, the 1st and 2nd kprobes are unregistered. At this moment, > ->nused is 8 but slot_used[9] is still used. To unregister this 10th > kprobe, we have to access slot_used[9]. Ah, I totally missed that bit of the code, sorry about that. Thanks for the explanation! > So let's just revert the commit 0888460c9050. Reverting that change sounds totally reasonable to me based on the above. Will you take care of that? For what it's worth, I think patch #2 should still be applicable, if you are okay with that one. Cheers, Nathan
On Wed, 30 Oct 2024 20:37:31 -0700 Nathan Chancellor <nathan@kernel.org> wrote: > On Thu, Oct 31, 2024 at 10:58:27AM +0900, Masami Hiramatsu wrote: > > On Wed, 30 Oct 2024 09:14:48 -0700 > > Nathan Chancellor <nathan@kernel.org> wrote: > > > > > Commit 0888460c9050 ("kprobes: Annotate structs with __counted_by()") > > > added a __counted_by annotation without adjusting the code for the > > > __counted_by requirements, resulting in a panic when UBSAN_BOUNDS and > > > FORTIFY_SOURCE are enabled: > > > > > > | memset: detected buffer overflow: 512 byte write of buffer size 0 > > > | WARNING: CPU: 0 PID: 1 at lib/string_helpers.c:1032 __fortify_report+0x64/0x80 > > > | Call Trace: > > > | __fortify_report+0x60/0x80 (unreliable) > > > | __fortify_panic+0x18/0x1c > > > | __get_insn_slot+0x33c/0x340 > > > > > > __counted_by requires that the counter be set before accessing the > > > flexible array but ->nused is not set until after ->slot_used is > > > accessed via memset(). Even if the current ->nused assignment were moved > > > up before memset(), the value of 1 would be incorrect because the entire > > > array is being accessed, not just one element. > > > > Ah, I think I misunderstood the __counted_by(). If so, ->nused can be > > smaller than the accessing element of slot_used[]. I should revert it. > > The accessing index and ->nused should have no relationship. > > > > for example, slots_per_page(c) is 10, and 10 kprobes are registered > > and then, the 1st and 2nd kprobes are unregistered. At this moment, > > ->nused is 8 but slot_used[9] is still used. To unregister this 10th > > kprobe, we have to access slot_used[9]. > > Ah, I totally missed that bit of the code, sorry about that. Thanks for > the explanation! > > > So let's just revert the commit 0888460c9050. > > Reverting that change sounds totally reasonable to me based on the > above. Will you take care of that? Yeah, probes/for-next is a working branch. So I just dropped it. > > For what it's worth, I think patch #2 should still be applicable, if you > are okay with that one. Yes, other patches look good to me. Thank you, > > Cheers, > Nathan
diff --git a/kernel/kprobes.c b/kernel/kprobes.c index 98d71a5acb723ddfff3efcc44cc6754ee36ec1de..2cf4628bc97ce2ae18547b513cd75b6350e9cc9c 100644 --- a/kernel/kprobes.c +++ b/kernel/kprobes.c @@ -145,16 +145,18 @@ kprobe_opcode_t *__get_insn_slot(struct kprobe_insn_cache *c) { struct kprobe_insn_page *kip; kprobe_opcode_t *slot = NULL; + int num_slots; /* Since the slot array is not protected by rcu, we need a mutex */ mutex_lock(&c->mutex); + num_slots = slots_per_page(c); retry: rcu_read_lock(); list_for_each_entry_rcu(kip, &c->pages, list) { - if (kip->nused < slots_per_page(c)) { + if (kip->nused < num_slots) { int i; - for (i = 0; i < slots_per_page(c); i++) { + for (i = 0; i < num_slots; i++) { if (kip->slot_used[i] == SLOT_CLEAN) { kip->slot_used[i] = SLOT_USED; kip->nused++; @@ -164,7 +166,7 @@ kprobe_opcode_t *__get_insn_slot(struct kprobe_insn_cache *c) } } /* kip->nused is broken. Fix it. */ - kip->nused = slots_per_page(c); + kip->nused = num_slots; WARN_ON(1); } } @@ -175,7 +177,7 @@ kprobe_opcode_t *__get_insn_slot(struct kprobe_insn_cache *c) goto retry; /* All out of space. Need to allocate a new page. */ - kip = kmalloc(KPROBE_INSN_PAGE_SIZE(slots_per_page(c)), GFP_KERNEL); + kip = kmalloc(KPROBE_INSN_PAGE_SIZE(num_slots), GFP_KERNEL); if (!kip) goto out; @@ -185,9 +187,11 @@ kprobe_opcode_t *__get_insn_slot(struct kprobe_insn_cache *c) goto out; } INIT_LIST_HEAD(&kip->list); - memset(kip->slot_used, SLOT_CLEAN, slots_per_page(c)); - kip->slot_used[0] = SLOT_USED; + /* nused must be set before accessing slot_used */ + kip->nused = num_slots; + memset(kip->slot_used, SLOT_CLEAN, num_slots); kip->nused = 1; + kip->slot_used[0] = SLOT_USED; kip->ngarbage = 0; kip->cache = c; list_add_rcu(&kip->list, &c->pages);
Commit 0888460c9050 ("kprobes: Annotate structs with __counted_by()") added a __counted_by annotation without adjusting the code for the __counted_by requirements, resulting in a panic when UBSAN_BOUNDS and FORTIFY_SOURCE are enabled: | memset: detected buffer overflow: 512 byte write of buffer size 0 | WARNING: CPU: 0 PID: 1 at lib/string_helpers.c:1032 __fortify_report+0x64/0x80 | Call Trace: | __fortify_report+0x60/0x80 (unreliable) | __fortify_panic+0x18/0x1c | __get_insn_slot+0x33c/0x340 __counted_by requires that the counter be set before accessing the flexible array but ->nused is not set until after ->slot_used is accessed via memset(). Even if the current ->nused assignment were moved up before memset(), the value of 1 would be incorrect because the entire array is being accessed, not just one element. Set ->nused to the full number of slots from slots_per_page() before calling memset() to resolve the panic. While it is not strictly necessary because of the new assignment, move the existing ->nused assignment above accessing ->slot_used[0] for visual consistency. The value of slots_per_page() should not change throughout __get_insn_slot() because ->insn_size is never modified after its initial assignment (which has to be done by this point otherwise it would be incorrect) and the other values are constants, so use a new variable to reuse its value directly. Fixes: 0888460c9050 ("kprobes: Annotate structs with __counted_by()") Signed-off-by: Nathan Chancellor <nathan@kernel.org> --- kernel/kprobes.c | 16 ++++++++++------ 1 file changed, 10 insertions(+), 6 deletions(-)