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bpf: add security_file_mprotect() to sleepable_lsm_hooks BTF set

PATCH In review Matt Bobrowski 1 participant 2 messages Feb 1, 2024

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BPF Security (LSM) BPF LSM
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Matt Bobrowski

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#0 lore raw

PATCH 1/1 bpf: add security_file_mprotect() to sleepable_lsm_hooks BTF set

security_file_mprotect() is missing from the sleepable_lsm_hooks BTF set. Add it so that operations performed by a BPF program which may result in the thread being put to sleep are permitted.

Building a kernel with the DEBUG_ATOMIC_SLEEP confiuration option enabled and running reasonable workloads stimulating a BPF program attached to security_file_mprotect() which could end up performing an operation that could sleep resulted in no splats.

Signed-off-by Matt Bobrowski <[email protected]>
---
 kernel/bpf/bpf_lsm.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)
kernel/bpf/bpf_lsm.c +3 -1
index 68240c3c6e7d..da52c955f3ca 100644
@@ -277,10 +277,13 @@ BTF_ID(func, bpf_lsm_bprm_creds_from_file)
 BTF_ID(func, bpf_lsm_capget)
 BTF_ID(func, bpf_lsm_capset)
 BTF_ID(func, bpf_lsm_cred_prepare)
+
 BTF_ID(func, bpf_lsm_file_ioctl)
 BTF_ID(func, bpf_lsm_file_lock)
 BTF_ID(func, bpf_lsm_file_open)
 BTF_ID(func, bpf_lsm_file_receive)
+BTF_ID(func, bpf_lsm_mmap_file)
+BTF_ID(func, bpf_lsm_file_mprotect)
 
 BTF_ID(func, bpf_lsm_inode_create)
 BTF_ID(func, bpf_lsm_inode_free_security)

@@ -316,7 +319,6 @@ BTF_ID(func, bpf_lsm_path_chown)
 BTF_ID(func, bpf_lsm_key_free)
 #endif /* CONFIG_KEYS */
 
-BTF_ID(func, bpf_lsm_mmap_file)
 BTF_ID(func, bpf_lsm_netlink_send)
 BTF_ID(func, bpf_lsm_path_notify)
 BTF_ID(func, bpf_lsm_release_secctx)
Signature · 3 lines
2.43.0.429.g432eaa2c6b-goog

/M
author
#1 lore raw
Quoted 8 lines · Matt Bobrowski

security_file_mprotect() is missing from the sleepable_lsm_hooks BTF set. Add it so that operations performed by a BPF program which may result in the thread being put to sleep are permitted.

Building a kernel with the DEBUG_ATOMIC_SLEEP confiuration option enabled and running reasonable workloads stimulating a BPF program attached to security_file_mprotect() which could end up performing an operation that could sleep resulted in no splats.

Actually, no, please disregard this patch. It was only a matter of timing before something had popped up.

This was sent out far too prematurely and I failed to realize that __bpf_prog_enter_sleepable() calls might_fault() and security_file_mprotect() is being called from a context whereby a mmap_lock is already being held. In essence, this also means that it's not possible to run sleepable BPF programs in contexts where a mmap_lock is already held as the page fault handler also attempts to take the mmap_lock, and well all know what happens when you have the same thread attempting to acquire the same lock whilst already holding that lock.

Quoted 33 lines
Signed-off-by Matt Bobrowski <[email protected]>
---
 kernel/bpf/bpf_lsm.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)
kernel/bpf/bpf_lsm.c +3 -1
index 68240c3c6e7d..da52c955f3ca 100644
@@ -277,10 +277,13 @@ BTF_ID(func, bpf_lsm_bprm_creds_from_file)
 BTF_ID(func, bpf_lsm_capget)
 BTF_ID(func, bpf_lsm_capset)
 BTF_ID(func, bpf_lsm_cred_prepare)
+
 BTF_ID(func, bpf_lsm_file_ioctl)
 BTF_ID(func, bpf_lsm_file_lock)
 BTF_ID(func, bpf_lsm_file_open)
 BTF_ID(func, bpf_lsm_file_receive)
+BTF_ID(func, bpf_lsm_mmap_file)
+BTF_ID(func, bpf_lsm_file_mprotect)
 
 BTF_ID(func, bpf_lsm_inode_create)
 BTF_ID(func, bpf_lsm_inode_free_security)

@@ -316,7 +319,6 @@ BTF_ID(func, bpf_lsm_path_chown)
 BTF_ID(func, bpf_lsm_key_free)
 #endif /* CONFIG_KEYS */
 
-BTF_ID(func, bpf_lsm_mmap_file)
 BTF_ID(func, bpf_lsm_netlink_send)
 BTF_ID(func, bpf_lsm_path_notify)
 BTF_ID(func, bpf_lsm_release_secctx)
Signature · 1 line
2.43.0.429.g432eaa2c6b-goog

/M