For clarity. It's increasingly hard to reason about the code, when KASLR
is moving around the boundaries. In this case where KASLR is randomizing
the location of the kernel image within physical memory, the maximum
number of address bits for physical memory has not changed.
What has changed is the ending address of memory that is allowed to be
directly mapped by the kernel.
Let's name the variable, and the associated macro accordingly.
Also, enhance the comment above the direct_map_physmem_end definition,
to further clarify how this all works.
Link: https://lkml.kernel.org/r/20241009025024.89813-1-jhubbard@nvidia.com
Signed-off-by: John Hubbard <jhubbard@nvidia.com>
Reviewed-by: Pankaj Gupta <pankaj.gupta@amd.com>
Acked-by: David Hildenbrand <david@redhat.com>
Acked-by: Will Deacon <will@kernel.org>
Reviewed-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Alistair Popple <apopple@nvidia.com>
Cc: Jordan Niethe <jniethe@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
mm_access() can return NULL if the mm is not found, but this is handled
the same as an error in all callers, with some translating this into an
-ESRCH error.
Only proc_mem_open() returns NULL if no mm is found, however in this case
it is clearer and makes more sense to explicitly handle the error.
Additionally we take the opportunity to refactor the function to eliminate
unnecessary nesting.
Simplify things by simply returning -ESRCH if no mm is found - this both
eliminates confusing use of the IS_ERR_OR_NULL() macro, and simplifies
callers which would return -ESRCH by returning this error directly.
[lorenzo.stoakes@oracle.com: prefer neater pointer error comparison]
Link: https://lkml.kernel.org/r/2fae1834-749a-45e1-8594-5e5979cf7103@lucifer.local
Link: https://lkml.kernel.org/r/20240924201023.193135-1-lorenzo.stoakes@oracle.com
Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Suggested-by: Arnd Bergmann <arnd@arndb.de>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Pull timer fix from Thomas Gleixner:
"A single fix for posix CPU timers.
When a thread is cloned, the posix CPU timers are not inherited.
If the parent has a CPU timer armed the corresponding tick dependency
in the tasks tick_dep_mask is set and copied to the new thread, which
means the new thread and all decendants will prevent the system to go
into full NOHZ operation.
Clear the tick dependency mask in copy_process() to fix this"
* tag 'timers-urgent-2024-11-03' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
posix-cpu-timers: Clear TICK_DEP_BIT_POSIX_TIMER on clone
Pull scheduler fixes from Thomas Gleixner:
- Plug a race between pick_next_task_fair() and try_to_wake_up() where
both try to write to the same task, even though both paths hold a
runqueue lock, but obviously from different runqueues.
The problem is that the store to task::on_rq in __block_task() is
visible to try_to_wake_up() which assumes that the task is not
queued. Both sides then operate on the same task.
Cure it by rearranging __block_task() so the the store to task::on_rq
is the last operation on the task.
- Prevent a potential NULL pointer dereference in task_numa_work()
task_numa_work() iterates the VMAs of a process. A concurrent unmap
of the address space can result in a NULL pointer return from
vma_next() which is unchecked.
Add the missing NULL pointer check to prevent this.
- Operate on the correct scheduler policy in task_should_scx()
task_should_scx() returns true when a task should be handled by sched
EXT. It checks the tasks scheduling policy.
This fails when the check is done before a policy has been set.
Cure it by handing the policy into task_should_scx() so it operates
on the requested value.
- Add the missing handling of sched EXT in the delayed dequeue
mechanism. This was simply forgotten.
* tag 'sched-urgent-2024-11-03' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
sched/ext: Fix scx vs sched_delayed
sched: Pass correct scheduling policy to __setscheduler_class
sched/numa: Fix the potential null pointer dereference in task_numa_work()
sched: Fix pick_next_task_fair() vs try_to_wake_up() race
Pull perf fix from Thomas Gleixner:
"perf_event_clear_cpumask() uses list_for_each_entry_rcu() without
being in a RCU read side critical section, which triggers a
'suspicious RCU usage' warning.
It turns out that the list walk does not be RCU protected because the
write side lock is held in this context.
Change it to a regular list walk"
* tag 'perf-urgent-2024-11-03' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
perf: Fix missing RCU reader protection in perf_event_clear_cpumask()
Pull irq fixes from Thomas Gleixner:
- Fix an off-by-one error in the failure path of msi_domain_alloc(),
which causes the cleanup loop to terminate early and leaking the
first allocated interrupt.
- Handle a corner case in GIC-V4 versus a lazily mapped Virtual
Processing Element (VPE). If the VPE has not been mapped because the
guest has not yet emitted a mapping command, then the set_affinity()
callback returns an error code, which causes the vCPU management to
fail.
Return success in this case without touching the hardware. This will
be done later when the guest issues the mapping command.
* tag 'irq-urgent-2024-11-03' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
irqchip/gic-v4: Correctly deal with set_affinity on lazily-mapped VPEs
genirq/msi: Fix off-by-one error in msi_domain_alloc()
Pull bpf fixes from Daniel Borkmann:
- Fix BPF verifier to force a checkpoint when the program's jump
history becomes too long (Eduard Zingerman)
- Add several fixes to the BPF bits iterator addressing issues like
memory leaks and overflow problems (Hou Tao)
- Fix an out-of-bounds write in trie_get_next_key (Byeonguk Jeong)
- Fix BPF test infra's LIVE_FRAME frame update after a page has been
recycled (Toke Høiland-Jørgensen)
- Fix BPF verifier and undo the 40-bytes extra stack space for
bpf_fastcall patterns due to various bugs (Eduard Zingerman)
- Fix a BPF sockmap race condition which could trigger a NULL pointer
dereference in sock_map_link_update_prog (Cong Wang)
- Fix tcp_bpf_recvmsg_parser to retrieve seq_copied from tcp_sk under
the socket lock (Jiayuan Chen)
* tag 'bpf-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf:
bpf, test_run: Fix LIVE_FRAME frame update after a page has been recycled
selftests/bpf: Add three test cases for bits_iter
bpf: Use __u64 to save the bits in bits iterator
bpf: Check the validity of nr_words in bpf_iter_bits_new()
bpf: Add bpf_mem_alloc_check_size() helper
bpf: Free dynamically allocated bits in bpf_iter_bits_destroy()
bpf: disallow 40-bytes extra stack for bpf_fastcall patterns
selftests/bpf: Add test for trie_get_next_key()
bpf: Fix out-of-bounds write in trie_get_next_key()
selftests/bpf: Test with a very short loop
bpf: Force checkpoint when jmp history is too long
bpf: fix filed access without lock
sock_map: fix a NULL pointer dereference in sock_map_link_update_prog()
On 32-bit hosts (e.g., arm32), when a bpf program passes a u64 to
bpf_iter_bits_new(), bpf_iter_bits_new() will use bits_copy to store the
content of the u64. However, bits_copy is only 4 bytes, leading to stack
corruption.
The straightforward solution would be to replace u64 with unsigned long
in bpf_iter_bits_new(). However, this introduces confusion and problems
for 32-bit hosts because the size of ulong in bpf program is 8 bytes,
but it is treated as 4-bytes after passed to bpf_iter_bits_new().
Fix it by changing the type of both bits and bit_count from unsigned
long to u64. However, the change is not enough. The main reason is that
bpf_iter_bits_next() uses find_next_bit() to find the next bit and the
pointer passed to find_next_bit() is an unsigned long pointer instead
of a u64 pointer. For 32-bit little-endian host, it is fine but it is
not the case for 32-bit big-endian host. Because under 32-bit big-endian
host, the first iterated unsigned long will be the bits 32-63 of the u64
instead of the expected bits 0-31. Therefore, in addition to changing
the type, swap the two unsigned longs within the u64 for 32-bit
big-endian host.
Signed-off-by: Hou Tao <houtao1@huawei.com>
Link: https://lore.kernel.org/r/20241030100516.3633640-5-houtao@huaweicloud.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Check the validity of nr_words in bpf_iter_bits_new(). Without this
check, when multiplication overflow occurs for nr_bits (e.g., when
nr_words = 0x0400-0001, nr_bits becomes 64), stack corruption may occur
due to bpf_probe_read_kernel_common(..., nr_bytes = 0x2000-0008).
Fix it by limiting the maximum value of nr_words to 511. The value is
derived from the current implementation of BPF memory allocator. To
ensure compatibility if the BPF memory allocator's size limitation
changes in the future, use the helper bpf_mem_alloc_check_size() to
check whether nr_bytes is too larger. And return -E2BIG instead of
-ENOMEM for oversized nr_bytes.
Fixes: 4665415975 ("bpf: Add bits iterator")
Signed-off-by: Hou Tao <houtao1@huawei.com>
Link: https://lore.kernel.org/r/20241030100516.3633640-4-houtao@huaweicloud.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Introduce bpf_mem_alloc_check_size() to check whether the allocation
size exceeds the limitation for the kmalloc-equivalent allocator. The
upper limit for percpu allocation is LLIST_NODE_SZ bytes larger than
non-percpu allocation, so a percpu argument is added to the helper.
The helper will be used in the following patch to check whether the size
parameter passed to bpf_mem_alloc() is too big.
Signed-off-by: Hou Tao <houtao1@huawei.com>
Link: https://lore.kernel.org/r/20241030100516.3633640-3-houtao@huaweicloud.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
bpf_iter_bits_destroy() uses "kit->nr_bits <= 64" to check whether the
bits are dynamically allocated. However, the check is incorrect and may
cause a kmemleak as shown below:
unreferenced object 0xffff88812628c8c0 (size 32):
comm "swapper/0", pid 1, jiffies 4294727320
hex dump (first 32 bytes):
b0 c1 55 f5 81 88 ff ff f0 f0 f0 f0 f0 f0 f0 f0 ..U...........
f0 f0 f0 f0 f0 f0 f0 f0 00 00 00 00 00 00 00 00 ..............
backtrace (crc 781e32cc):
[<00000000c452b4ab>] kmemleak_alloc+0x4b/0x80
[<0000000004e09f80>] __kmalloc_node_noprof+0x480/0x5c0
[<00000000597124d6>] __alloc.isra.0+0x89/0xb0
[<000000004ebfffcd>] alloc_bulk+0x2af/0x720
[<00000000d9c10145>] prefill_mem_cache+0x7f/0xb0
[<00000000ff9738ff>] bpf_mem_alloc_init+0x3e2/0x610
[<000000008b616eac>] bpf_global_ma_init+0x19/0x30
[<00000000fc473efc>] do_one_initcall+0xd3/0x3c0
[<00000000ec81498c>] kernel_init_freeable+0x66a/0x940
[<00000000b119f72f>] kernel_init+0x20/0x160
[<00000000f11ac9a7>] ret_from_fork+0x3c/0x70
[<0000000004671da4>] ret_from_fork_asm+0x1a/0x30
That is because nr_bits will be set as zero in bpf_iter_bits_next()
after all bits have been iterated.
Fix the issue by setting kit->bit to kit->nr_bits instead of setting
kit->nr_bits to zero when the iteration completes in
bpf_iter_bits_next(). In addition, use "!nr_bits || bits >= nr_bits" to
check whether the iteration is complete and still use "nr_bits > 64" to
indicate whether bits are dynamically allocated. The "!nr_bits" check is
necessary because bpf_iter_bits_new() may fail before setting
kit->nr_bits, and this condition will stop the iteration early instead
of accessing the zeroed or freed kit->bits.
Considering the initial value of kit->bits is -1 and the type of
kit->nr_bits is unsigned int, change the type of kit->nr_bits to int.
The potential overflow problem will be handled in the following patch.
Fixes: 4665415975 ("bpf: Add bits iterator")
Acked-by: Yafang Shao <laoar.shao@gmail.com>
Signed-off-by: Hou Tao <houtao1@huawei.com>
Link: https://lore.kernel.org/r/20241030100516.3633640-2-houtao@huaweicloud.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Pull cgroup fixes from Tejun Heo:
- cgroup_bpf_release_fn() could saturate system_wq with
cgrp->bpf.release_work which can then form a circular dependency
leading to deadlocks. Fix by using a dedicated workqueue. The
system_wq's max concurrency limit is being increased separately.
- Fix theoretical off-by-one bug when enforcing max cgroup hierarchy
depth
* tag 'cgroup-for-6.12-rc5-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/cgroup:
cgroup: Fix potential overflow issue when checking max_depth
cgroup/bpf: use a dedicated workqueue for cgroup bpf destruction
Pull sched_ext fixes from Tejun Heo:
- Instances of scx_ops_bypass() could race each other leading to
misbehavior. Fix by protecting the operation with a spinlock.
- selftest and userspace header fixes
* tag 'sched_ext-for-6.12-rc5-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/sched_ext:
sched_ext: Fix enq_last_no_enq_fails selftest
sched_ext: Make cast_mask() inline
scx: Fix raciness in scx_ops_bypass()
scx: Fix exit selftest to use custom DSQ
sched_ext: Fix function pointer type mismatches in BPF selftests
selftests/sched_ext: add order-only dependency of runner.o on BPFOBJ
trie_get_next_key() allocates a node stack with size trie->max_prefixlen,
while it writes (trie->max_prefixlen + 1) nodes to the stack when it has
full paths from the root to leaves. For example, consider a trie with
max_prefixlen is 8, and the nodes with key 0x00/0, 0x00/1, 0x00/2, ...
0x00/8 inserted. Subsequent calls to trie_get_next_key with _key with
.prefixlen = 8 make 9 nodes be written on the node stack with size 8.
Fixes: b471f2f1de ("bpf: implement MAP_GET_NEXT_KEY command for LPM_TRIE map")
Signed-off-by: Byeonguk Jeong <jungbu2855@gmail.com>
Reviewed-by: Toke Høiland-Jørgensen <toke@kernel.org>
Tested-by: Hou Tao <houtao1@huawei.com>
Acked-by: Hou Tao <houtao1@huawei.com>
Link: https://lore.kernel.org/r/Zxx384ZfdlFYnz6J@localhost.localdomain
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
A specifically crafted program might trick verifier into growing very
long jump history within a single bpf_verifier_state instance.
Very long jump history makes mark_chain_precision() unreasonably slow,
especially in case if verifier processes a loop.
Mitigate this by forcing new state in is_state_visited() in case if
current state's jump history is too long.
Use same constant as in `skip_inf_loop_check`, but multiply it by
arbitrarily chosen value 2 to account for jump history containing not
only information about jumps, but also information about stack access.
For an example of problematic program consider the code below,
w/o this patch the example is processed by verifier for ~15 minutes,
before failing to allocate big-enough chunk for jmp_history.
0: r7 = *(u16 *)(r1 +0);"
1: r7 += 0x1ab064b9;"
2: if r7 & 0x702000 goto 1b;
3: r7 &= 0x1ee60e;"
4: r7 += r1;"
5: if r7 s> 0x37d2 goto +0;"
6: r0 = 0;"
7: exit;"
Perf profiling shows that most of the time is spent in
mark_chain_precision() ~95%.
The easiest way to explain why this program causes problems is to
apply the following patch:
diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 0c216e71cec7..4b4823961abe 100644
\--- a/include/linux/bpf.h
\+++ b/include/linux/bpf.h
\@@ -1926,7 +1926,7 @@ struct bpf_array {
};
};
-#define BPF_COMPLEXITY_LIMIT_INSNS 1000000 /* yes. 1M insns */
+#define BPF_COMPLEXITY_LIMIT_INSNS 256 /* yes. 1M insns */
#define MAX_TAIL_CALL_CNT 33
/* Maximum number of loops for bpf_loop and bpf_iter_num.
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index f514247ba8ba..75e88be3bb3e 100644
\--- a/kernel/bpf/verifier.c
\+++ b/kernel/bpf/verifier.c
\@@ -18024,8 +18024,13 @@ static int is_state_visited(struct bpf_verifier_env *env, int insn_idx)
skip_inf_loop_check:
if (!force_new_state &&
env->jmps_processed - env->prev_jmps_processed < 20 &&
- env->insn_processed - env->prev_insn_processed < 100)
+ env->insn_processed - env->prev_insn_processed < 100) {
+ verbose(env, "is_state_visited: suppressing checkpoint at %d, %d jmps processed, cur->jmp_history_cnt is %d\n",
+ env->insn_idx,
+ env->jmps_processed - env->prev_jmps_processed,
+ cur->jmp_history_cnt);
add_new_state = false;
+ }
goto miss;
}
/* If sl->state is a part of a loop and this loop's entry is a part of
\@@ -18142,6 +18147,9 @@ static int is_state_visited(struct bpf_verifier_env *env, int insn_idx)
if (!add_new_state)
return 0;
+ verbose(env, "is_state_visited: new checkpoint at %d, resetting env->jmps_processed\n",
+ env->insn_idx);
+
/* There were no equivalent states, remember the current one.
* Technically the current state is not proven to be safe yet,
* but it will either reach outer most bpf_exit (which means it's safe)
And observe verification log:
...
is_state_visited: new checkpoint at 5, resetting env->jmps_processed
5: R1=ctx() R7=ctx(...)
5: (65) if r7 s> 0x37d2 goto pc+0 ; R7=ctx(...)
6: (b7) r0 = 0 ; R0_w=0
7: (95) exit
from 5 to 6: R1=ctx() R7=ctx(...) R10=fp0
6: R1=ctx() R7=ctx(...) R10=fp0
6: (b7) r0 = 0 ; R0_w=0
7: (95) exit
is_state_visited: suppressing checkpoint at 1, 3 jmps processed, cur->jmp_history_cnt is 74
from 2 to 1: R1=ctx() R7_w=scalar(...) R10=fp0
1: R1=ctx() R7_w=scalar(...) R10=fp0
1: (07) r7 += 447767737
is_state_visited: suppressing checkpoint at 2, 3 jmps processed, cur->jmp_history_cnt is 75
2: R7_w=scalar(...)
2: (45) if r7 & 0x702000 goto pc-2
... mark_precise 152 steps for r7 ...
2: R7_w=scalar(...)
is_state_visited: suppressing checkpoint at 1, 4 jmps processed, cur->jmp_history_cnt is 75
1: (07) r7 += 447767737
is_state_visited: suppressing checkpoint at 2, 4 jmps processed, cur->jmp_history_cnt is 76
2: R7_w=scalar(...)
2: (45) if r7 & 0x702000 goto pc-2
...
BPF program is too large. Processed 257 insn
The log output shows that checkpoint at label (1) is never created,
because it is suppressed by `skip_inf_loop_check` logic:
a. When 'if' at (2) is processed it pushes a state with insn_idx (1)
onto stack and proceeds to (3);
b. At (5) checkpoint is created, and this resets
env->{jmps,insns}_processed.
c. Verification proceeds and reaches `exit`;
d. State saved at step (a) is popped from stack and is_state_visited()
considers if checkpoint needs to be added, but because
env->{jmps,insns}_processed had been just reset at step (b)
the `skip_inf_loop_check` logic forces `add_new_state` to false.
e. Verifier proceeds with current state, which slowly accumulates
more and more entries in the jump history.
The accumulation of entries in the jump history is a problem because
of two factors:
- it eventually exhausts memory available for kmalloc() allocation;
- mark_chain_precision() traverses the jump history of a state,
meaning that if `r7` is marked precise, verifier would iterate
ever growing jump history until parent state boundary is reached.
(note: the log also shows a REG INVARIANTS VIOLATION warning
upon jset processing, but that's another bug to fix).
With this patch applied, the example above is rejected by verifier
under 1s of time, reaching 1M instructions limit.
The program is a simplified reproducer from syzbot report.
Previous discussion could be found at [1].
The patch does not cause any changes in verification performance,
when tested on selftests from veristat.cfg and cilium programs taken
from [2].
[1] https://lore.kernel.org/bpf/20241009021254.2805446-1-eddyz87@gmail.com/
[2] https://github.com/anakryiko/cilium
Changelog:
- v1 -> v2:
- moved patch to bpf tree;
- moved force_new_state variable initialization after declaration and
shortened the comment.
v1: https://lore.kernel.org/bpf/20241018020307.1766906-1-eddyz87@gmail.com/
Fixes: 2589726d12 ("bpf: introduce bounded loops")
Reported-by: syzbot+7e46cdef14bf496a3ab4@syzkaller.appspotmail.com
Signed-off-by: Eduard Zingerman <eddyz87@gmail.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20241029172641.1042523-1-eddyz87@gmail.com
Closes: https://lore.kernel.org/bpf/670429f6.050a0220.49194.0517.GAE@google.com/
Commit 98442f0ccd ("sched: Fix delayed_dequeue vs
switched_from_fair()") overlooked that __setscheduler_prio(), now
__setscheduler_class() relies on p->policy for task_should_scx(), and
moved the call before __setscheduler_params() updates it, causing it
to be using the old p->policy value.
Resolve this by changing task_should_scx() to take the policy itself
instead of a task pointer, such that __sched_setscheduler() can pass
in the updated policy.
Fixes: 98442f0ccd ("sched: Fix delayed_dequeue vs switched_from_fair()")
Signed-off-by: Aboorva Devarajan <aboorvad@linux.ibm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Tejun Heo <tj@kernel.org>
There is no reason to invoke these hooks early against an mm that is in an
incomplete state.
The change in commit d240629148 ("fork: use __mt_dup() to duplicate
maple tree in dup_mmap()") makes this more pertinent as we may be in a
state where entries in the maple tree are not yet consistent.
Their placement early in dup_mmap() only appears to have been meaningful
for early error checking, and since functionally it'd require a very small
allocation to fail (in practice 'too small to fail') that'd only occur in
the most dire circumstances, meaning the fork would fail or be OOM'd in
any case.
Since both khugepaged and KSM tracking are there to provide optimisations
to memory performance rather than critical functionality, it doesn't
really matter all that much if, under such dire memory pressure, we fail
to register an mm with these.
As a result, we follow the example of commit d2081b2bf8 ("mm:
khugepaged: make khugepaged_enter() void function") and make ksm_fork() a
void function also.
We only expose the mm to these functions once we are done with them and
only if no error occurred in the fork operation.
Link: https://lkml.kernel.org/r/e0cb8b840c9d1d5a6e84d4f8eff5f3f2022aa10c.1729014377.git.lorenzo.stoakes@oracle.com
Fixes: d240629148 ("fork: use __mt_dup() to duplicate maple tree in dup_mmap()")
Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Reported-by: Jann Horn <jannh@google.com>
Reviewed-by: Liam R. Howlett <Liam.Howlett@Oracle.com>
Reviewed-by: Vlastimil Babka <vbabka@suse.cz>
Reviewed-by: Jann Horn <jannh@google.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Jan Kara <jack@suse.cz>
Cc: Linus Torvalds <torvalds@linuxfoundation.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Patch series "fork: do not expose incomplete mm on fork".
During fork we may place the virtual memory address space into an
inconsistent state before the fork operation is complete.
In addition, we may encounter an error during the fork operation that
indicates that the virtual memory address space is invalidated.
As a result, we should not be exposing it in any way to external machinery
that might interact with the mm or VMAs, machinery that is not designed to
deal with incomplete state.
We specifically update the fork logic to defer khugepaged and ksm to the
end of the operation and only to be invoked if no error arose, and
disallow uffd from observing fork events should an error have occurred.
This patch (of 2):
Currently on fork we expose the virtual address space of a process to
userland unconditionally if uffd is registered in VMAs, regardless of
whether an error arose in the fork.
This is performed in dup_userfaultfd_complete() which is invoked
unconditionally, and performs two duties - invoking registered handlers
for the UFFD_EVENT_FORK event via dup_fctx(), and clearing down
userfaultfd_fork_ctx objects established in dup_userfaultfd().
This is problematic, because the virtual address space may not yet be
correctly initialised if an error arose.
The change in commit d240629148 ("fork: use __mt_dup() to duplicate
maple tree in dup_mmap()") makes this more pertinent as we may be in a
state where entries in the maple tree are not yet consistent.
We address this by, on fork error, ensuring that we roll back state that
we would otherwise expect to clean up through the event being handled by
userland and perform the memory freeing duty otherwise performed by
dup_userfaultfd_complete().
We do this by implementing a new function, dup_userfaultfd_fail(), which
performs the same loop, only decrementing reference counts.
Note that we perform mmgrab() on the parent and child mm's, however
userfaultfd_ctx_put() will mmdrop() this once the reference count drops to
zero, so we will avoid memory leaks correctly here.
Link: https://lkml.kernel.org/r/cover.1729014377.git.lorenzo.stoakes@oracle.com
Link: https://lkml.kernel.org/r/d3691d58bb58712b6fb3df2be441d175bd3cdf07.1729014377.git.lorenzo.stoakes@oracle.com
Fixes: d240629148 ("fork: use __mt_dup() to duplicate maple tree in dup_mmap()")
Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Reported-by: Jann Horn <jannh@google.com>
Reviewed-by: Jann Horn <jannh@google.com>
Reviewed-by: Liam R. Howlett <Liam.Howlett@Oracle.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Jan Kara <jack@suse.cz>
Cc: Linus Torvalds <torvalds@linuxfoundation.org>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
