Hi, Enclosed are a pair of patches for an oops that can occur if an exception is generated while a bpf subprogram is running. One of the bpf_prog_aux entries for the subprograms are missing an extable. This can lead to an exception that would otherwise be handled turning into a NULL pointer bug.
These changes were tested via the verifier and progs selftests and no regressions were observed.
Changes from v3: - Selftest style fixups (Feedback from Yonghong Song) - Selftest needs to assert that test bpf program executed (Feedback from Yonghong Song) - Selftest should combine open and load using open_and_load (Feedback from Yonghong Song)
Changes from v2: - Insert only the main program's kallsyms (Feedback from Yonghong Song and Alexei Starovoitov) - Selftest should use ASSERT instead of CHECK (Feedback from Yonghong Song) - Selftest needs some cleanup (Feedback from Yonghong Song) - Switch patch order (Feedback from Alexei Starovoitov)
Changes from v1: - Add a selftest (Feedback From Alexei Starovoitov) - Move to a 1-line verifier change instead of searching multiple extables
Krister Johansen (2): bpf: ensure main program has an extable selftests/bpf: add a test for subprogram extables
kernel/bpf/verifier.c | 6 ++- .../bpf/prog_tests/subprogs_extable.c | 29 +++++++++++ .../bpf/progs/test_subprogs_extable.c | 51 +++++++++++++++++++ 3 files changed, 84 insertions(+), 2 deletions(-) create mode 100644 tools/testing/selftests/bpf/prog_tests/subprogs_extable.c create mode 100644 tools/testing/selftests/bpf/progs/test_subprogs_extable.c
When subprograms are in use, the main program is not jit'd after the subprograms because jit_subprogs sets a value for prog->bpf_func upon success. Subsequent calls to the JIT are bypassed when this value is non-NULL. This leads to a situation where the main program and its func[0] counterpart are both in the bpf kallsyms tree, but only func[0] has an extable. Extables are only created during JIT. Now there are two nearly identical program ksym entries in the tree, but only one has an extable. Depending upon how the entries are placed, there's a chance that a fault will call search_extable on the aux with the NULL entry.
Since jit_subprogs already copies state from func[0] to the main program, include the extable pointer in this state duplication. Additionally, ensure that the copy of the main program in func[0] is not added to the bpf_prog_kallsyms table. Instead, let the main program get added later in bpf_prog_load(). This ensures there is only a single copy of the main program in the kallsyms table, and that its tag matches the tag observed by tooling like bpftool.
Cc: stable@vger.kernel.org Fixes: 1c2a088a6626 ("bpf: x64: add JIT support for multi-function programs") Signed-off-by: Krister Johansen kjlx@templeofstupid.com Acked-by: Yonghong Song yhs@fb.com --- kernel/bpf/verifier.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-)
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index 5871aa78d01a..b62d1fc0f92b 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -17214,9 +17214,10 @@ static int jit_subprogs(struct bpf_verifier_env *env) }
/* finally lock prog and jit images for all functions and - * populate kallsysm + * populate kallsysm. Begin at the first subprogram, since + * bpf_prog_load will add the kallsyms for the main program. */ - for (i = 0; i < env->subprog_cnt; i++) { + for (i = 1; i < env->subprog_cnt; i++) { bpf_prog_lock_ro(func[i]); bpf_prog_kallsyms_add(func[i]); } @@ -17242,6 +17243,7 @@ static int jit_subprogs(struct bpf_verifier_env *env) prog->jited = 1; prog->bpf_func = func[0]->bpf_func; prog->jited_len = func[0]->jited_len; + prog->aux->extable = func[0]->aux->extable; prog->aux->func = func; prog->aux->func_cnt = env->subprog_cnt; bpf_prog_jit_attempt_done(prog);
In certain situations a program with subprograms may have a NULL extable entry. This should not happen, and when it does, it turns a single trap into multiple. Add a test case for further debugging and to prevent regressions.
The test-case contains three essentially identical versions of the same test because just one program may not be sufficient to trigger the oops. This is due to the fact that the items are stored in a binary tree and have identical values so it's possible to sometimes find the ksym with the extable. With 3 copies, this has been reliable on this author's test systems.
When triggered out of this test case, the oops looks like this:
BUG: kernel NULL pointer dereference, address: 000000000000000c #PF: supervisor read access in kernel mode #PF: error_code(0x0000) - not-present page PGD 0 P4D 0 Oops: 0000 [#1] PREEMPT SMP NOPTI CPU: 0 PID: 1132 Comm: test_progs Tainted: G OE 6.4.0-rc3+ #2 RIP: 0010:cmp_ex_search+0xb/0x30 Code: cc cc cc cc e8 36 cb 03 00 66 0f 1f 44 00 00 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 f3 0f 1e fa 55 48 89 e5 48 8b 07 <48> 63 0e 48 01 f1 31 d2 48 39 c8 19 d2 48 39 c8 b8 01 00 00 00 0f RSP: 0018:ffffb30c4291f998 EFLAGS: 00010006 RAX: ffffffffc00b49da RBX: 0000000000000002 RCX: 000000000000000c RDX: 0000000000000002 RSI: 000000000000000c RDI: ffffb30c4291f9e8 RBP: ffffb30c4291f998 R08: ffffffffab1a42d0 R09: 0000000000000001 R10: 0000000000000000 R11: ffffffffab1a42d0 R12: ffffb30c4291f9e8 R13: 000000000000000c R14: 000000000000000c R15: 0000000000000000 FS: 00007fb5d9e044c0(0000) GS:ffff92e95ee00000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 000000000000000c CR3: 000000010c3a2005 CR4: 00000000007706f0 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 PKRU: 55555554 Call Trace: <TASK> bsearch+0x41/0x90 ? __pfx_cmp_ex_search+0x10/0x10 ? bpf_prog_45a7907e7114d0ff_handle_fexit_ret_subprogs3+0x2a/0x6c search_extable+0x3b/0x60 ? bpf_prog_45a7907e7114d0ff_handle_fexit_ret_subprogs3+0x2a/0x6c search_bpf_extables+0x10d/0x190 ? bpf_prog_45a7907e7114d0ff_handle_fexit_ret_subprogs3+0x2a/0x6c search_exception_tables+0x5d/0x70 fixup_exception+0x3f/0x5b0 ? look_up_lock_class+0x61/0x110 ? __lock_acquire+0x6b8/0x3560 ? __lock_acquire+0x6b8/0x3560 ? __lock_acquire+0x6b8/0x3560 kernelmode_fixup_or_oops+0x46/0x110 __bad_area_nosemaphore+0x68/0x2b0 ? __lock_acquire+0x6b8/0x3560 bad_area_nosemaphore+0x16/0x20 do_kern_addr_fault+0x81/0xa0 exc_page_fault+0xd6/0x210 asm_exc_page_fault+0x2b/0x30 RIP: 0010:bpf_prog_45a7907e7114d0ff_handle_fexit_ret_subprogs3+0x2a/0x6c Code: f3 0f 1e fa 0f 1f 44 00 00 66 90 55 48 89 e5 f3 0f 1e fa 48 8b 7f 08 49 bb 00 00 00 00 00 80 00 00 4c 39 df 73 04 31 f6 eb 04 <48> 8b 77 00 49 bb 00 00 00 00 00 80 00 00 48 81 c7 7c 00 00 00 4c RSP: 0018:ffffb30c4291fcb8 EFLAGS: 00010282 RAX: 0000000000000001 RBX: 0000000000000001 RCX: 0000000000000000 RDX: 00000000cddf1af1 RSI: 000000005315a00d RDI: ffffffffffffffea RBP: ffffb30c4291fcb8 R08: ffff92e644bf38a8 R09: 0000000000000000 R10: 0000000000000000 R11: 0000800000000000 R12: ffff92e663652690 R13: 00000000000001c8 R14: 00000000000001c8 R15: 0000000000000003 bpf_trampoline_251255721842_2+0x63/0x1000 bpf_testmod_return_ptr+0x9/0xb0 [bpf_testmod] ? bpf_testmod_test_read+0x43/0x2d0 [bpf_testmod] sysfs_kf_bin_read+0x60/0x90 kernfs_fop_read_iter+0x143/0x250 vfs_read+0x240/0x2a0 ksys_read+0x70/0xe0 __x64_sys_read+0x1f/0x30 do_syscall_64+0x68/0xa0 ? syscall_exit_to_user_mode+0x77/0x1f0 ? do_syscall_64+0x77/0xa0 ? irqentry_exit+0x35/0xa0 ? sysvec_apic_timer_interrupt+0x4d/0x90 entry_SYSCALL_64_after_hwframe+0x72/0xdc RIP: 0033:0x7fb5da00a392 Code: ac 00 00 f7 d8 64 89 02 48 c7 c0 ff ff ff ff eb be 0f 1f 80 00 00 00 00 f3 0f 1e fa 64 8b 04 25 18 00 00 00 85 c0 75 10 0f 05 <48> 3d 00 f0 ff ff 77 56 c3 0f 1f 44 00 00 48 83 ec 28 48 89 54 24 RSP: 002b:00007ffc5b3cab68 EFLAGS: 00000246 ORIG_RAX: 0000000000000000 RAX: ffffffffffffffda RBX: 000055bee7b8b100 RCX: 00007fb5da00a392 RDX: 00000000000001c8 RSI: 0000000000000000 RDI: 0000000000000009 RBP: 00007ffc5b3caba0 R08: 0000000000000000 R09: 0000000000000037 R10: 000055bee7b8c2a7 R11: 0000000000000246 R12: 000055bee78f1f60 R13: 00007ffc5b3cae90 R14: 0000000000000000 R15: 0000000000000000 </TASK> Modules linked in: bpf_testmod(OE) nls_iso8859_1 dm_multipath scsi_dh_rdac scsi_dh_emc scsi_dh_alua intel_rapl_msr intel_rapl_common intel_uncore_frequency_common ppdev nfit crct10dif_pclmul crc32_pclmul psmouse ghash_clmulni_intel sha512_ssse3 aesni_intel parport_pc crypto_simd cryptd input_leds parport rapl ena i2c_piix4 mac_hid serio_raw ramoops reed_solomon pstore_blk drm pstore_zone efi_pstore autofs4 [last unloaded: bpf_testmod(OE)] CR2: 000000000000000c
Though there may be some variation, depending on which suprogram triggers the bug.
Signed-off-by: Krister Johansen kjlx@templeofstupid.com --- .../bpf/prog_tests/subprogs_extable.c | 29 +++++++++++ .../bpf/progs/test_subprogs_extable.c | 51 +++++++++++++++++++ 2 files changed, 80 insertions(+) create mode 100644 tools/testing/selftests/bpf/prog_tests/subprogs_extable.c create mode 100644 tools/testing/selftests/bpf/progs/test_subprogs_extable.c
diff --git a/tools/testing/selftests/bpf/prog_tests/subprogs_extable.c b/tools/testing/selftests/bpf/prog_tests/subprogs_extable.c new file mode 100644 index 000000000000..3afd9f775f68 --- /dev/null +++ b/tools/testing/selftests/bpf/prog_tests/subprogs_extable.c @@ -0,0 +1,29 @@ +// SPDX-License-Identifier: GPL-2.0 + +#include <test_progs.h> +#include "test_subprogs_extable.skel.h" + +void test_subprogs_extable(void) +{ + const int read_sz = 456; + struct test_subprogs_extable *skel; + int err; + + skel = test_subprogs_extable__open_and_load(); + if (!ASSERT_OK_PTR(skel, "skel_open_and_load")) + return; + + err = test_subprogs_extable__attach(skel); + if (!ASSERT_OK(err, "skel_attach")) + goto cleanup; + + /* trigger tracepoint */ + ASSERT_OK(trigger_module_test_read(read_sz), "trigger_read"); + + ASSERT_NEQ(skel->bss->triggered, 0, "verify at least one program ran"); + + test_subprogs_extable__detach(skel); + +cleanup: + test_subprogs_extable__destroy(skel); +} diff --git a/tools/testing/selftests/bpf/progs/test_subprogs_extable.c b/tools/testing/selftests/bpf/progs/test_subprogs_extable.c new file mode 100644 index 000000000000..e2a21fbd4e44 --- /dev/null +++ b/tools/testing/selftests/bpf/progs/test_subprogs_extable.c @@ -0,0 +1,51 @@ +// SPDX-License-Identifier: GPL-2.0 + +#include "vmlinux.h" +#include <bpf/bpf_helpers.h> +#include <bpf/bpf_tracing.h> + +struct { + __uint(type, BPF_MAP_TYPE_ARRAY); + __uint(max_entries, 8); + __type(key, __u32); + __type(value, __u64); +} test_array SEC(".maps"); + +unsigned int triggered; + +static __u64 test_cb(struct bpf_map *map, __u32 *key, __u64 *val, void *data) +{ + return 1; +} + +SEC("fexit/bpf_testmod_return_ptr") +int BPF_PROG(handle_fexit_ret_subprogs, int arg, struct file *ret) +{ + *(volatile long *)ret; + *(volatile int *)&ret->f_mode; + bpf_for_each_map_elem(&test_array, test_cb, NULL, 0); + triggered++; + return 0; +} + +SEC("fexit/bpf_testmod_return_ptr") +int BPF_PROG(handle_fexit_ret_subprogs2, int arg, struct file *ret) +{ + *(volatile long *)ret; + *(volatile int *)&ret->f_mode; + bpf_for_each_map_elem(&test_array, test_cb, NULL, 0); + triggered++; + return 0; +} + +SEC("fexit/bpf_testmod_return_ptr") +int BPF_PROG(handle_fexit_ret_subprogs3, int arg, struct file *ret) +{ + *(volatile long *)ret; + *(volatile int *)&ret->f_mode; + bpf_for_each_map_elem(&test_array, test_cb, NULL, 0); + triggered++; + return 0; +} + +char _license[] SEC("license") = "GPL";
On 6/9/23 2:40 PM, Krister Johansen wrote:
In certain situations a program with subprograms may have a NULL extable entry. This should not happen, and when it does, it turns a single trap into multiple. Add a test case for further debugging and to prevent regressions.
The test-case contains three essentially identical versions of the same test because just one program may not be sufficient to trigger the oops. This is due to the fact that the items are stored in a binary tree and have identical values so it's possible to sometimes find the ksym with the extable. With 3 copies, this has been reliable on this author's test systems.
When triggered out of this test case, the oops looks like this:
BUG: kernel NULL pointer dereference, address: 000000000000000c #PF: supervisor read access in kernel mode #PF: error_code(0x0000) - not-present page PGD 0 P4D 0 Oops: 0000 [#1] PREEMPT SMP NOPTI CPU: 0 PID: 1132 Comm: test_progs Tainted: G OE 6.4.0-rc3+ #2 RIP: 0010:cmp_ex_search+0xb/0x30 Code: cc cc cc cc e8 36 cb 03 00 66 0f 1f 44 00 00 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 f3 0f 1e fa 55 48 89 e5 48 8b 07 <48> 63 0e 48 01 f1 31 d2 48 39 c8 19 d2 48 39 c8 b8 01 00 00 00 0f RSP: 0018:ffffb30c4291f998 EFLAGS: 00010006 RAX: ffffffffc00b49da RBX: 0000000000000002 RCX: 000000000000000c RDX: 0000000000000002 RSI: 000000000000000c RDI: ffffb30c4291f9e8 RBP: ffffb30c4291f998 R08: ffffffffab1a42d0 R09: 0000000000000001 R10: 0000000000000000 R11: ffffffffab1a42d0 R12: ffffb30c4291f9e8 R13: 000000000000000c R14: 000000000000000c R15: 0000000000000000 FS: 00007fb5d9e044c0(0000) GS:ffff92e95ee00000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 000000000000000c CR3: 000000010c3a2005 CR4: 00000000007706f0 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 PKRU: 55555554 Call Trace: <TASK> bsearch+0x41/0x90 ? __pfx_cmp_ex_search+0x10/0x10 ? bpf_prog_45a7907e7114d0ff_handle_fexit_ret_subprogs3+0x2a/0x6c search_extable+0x3b/0x60 ? bpf_prog_45a7907e7114d0ff_handle_fexit_ret_subprogs3+0x2a/0x6c search_bpf_extables+0x10d/0x190 ? bpf_prog_45a7907e7114d0ff_handle_fexit_ret_subprogs3+0x2a/0x6c search_exception_tables+0x5d/0x70 fixup_exception+0x3f/0x5b0 ? look_up_lock_class+0x61/0x110 ? __lock_acquire+0x6b8/0x3560 ? __lock_acquire+0x6b8/0x3560 ? __lock_acquire+0x6b8/0x3560 kernelmode_fixup_or_oops+0x46/0x110 __bad_area_nosemaphore+0x68/0x2b0 ? __lock_acquire+0x6b8/0x3560 bad_area_nosemaphore+0x16/0x20 do_kern_addr_fault+0x81/0xa0 exc_page_fault+0xd6/0x210 asm_exc_page_fault+0x2b/0x30 RIP: 0010:bpf_prog_45a7907e7114d0ff_handle_fexit_ret_subprogs3+0x2a/0x6c Code: f3 0f 1e fa 0f 1f 44 00 00 66 90 55 48 89 e5 f3 0f 1e fa 48 8b 7f 08 49 bb 00 00 00 00 00 80 00 00 4c 39 df 73 04 31 f6 eb 04 <48> 8b 77 00 49 bb 00 00 00 00 00 80 00 00 48 81 c7 7c 00 00 00 4c RSP: 0018:ffffb30c4291fcb8 EFLAGS: 00010282 RAX: 0000000000000001 RBX: 0000000000000001 RCX: 0000000000000000 RDX: 00000000cddf1af1 RSI: 000000005315a00d RDI: ffffffffffffffea RBP: ffffb30c4291fcb8 R08: ffff92e644bf38a8 R09: 0000000000000000 R10: 0000000000000000 R11: 0000800000000000 R12: ffff92e663652690 R13: 00000000000001c8 R14: 00000000000001c8 R15: 0000000000000003 bpf_trampoline_251255721842_2+0x63/0x1000 bpf_testmod_return_ptr+0x9/0xb0 [bpf_testmod] ? bpf_testmod_test_read+0x43/0x2d0 [bpf_testmod] sysfs_kf_bin_read+0x60/0x90 kernfs_fop_read_iter+0x143/0x250 vfs_read+0x240/0x2a0 ksys_read+0x70/0xe0 __x64_sys_read+0x1f/0x30 do_syscall_64+0x68/0xa0 ? syscall_exit_to_user_mode+0x77/0x1f0 ? do_syscall_64+0x77/0xa0 ? irqentry_exit+0x35/0xa0 ? sysvec_apic_timer_interrupt+0x4d/0x90 entry_SYSCALL_64_after_hwframe+0x72/0xdc RIP: 0033:0x7fb5da00a392 Code: ac 00 00 f7 d8 64 89 02 48 c7 c0 ff ff ff ff eb be 0f 1f 80 00 00 00 00 f3 0f 1e fa 64 8b 04 25 18 00 00 00 85 c0 75 10 0f 05 <48> 3d 00 f0 ff ff 77 56 c3 0f 1f 44 00 00 48 83 ec 28 48 89 54 24 RSP: 002b:00007ffc5b3cab68 EFLAGS: 00000246 ORIG_RAX: 0000000000000000 RAX: ffffffffffffffda RBX: 000055bee7b8b100 RCX: 00007fb5da00a392 RDX: 00000000000001c8 RSI: 0000000000000000 RDI: 0000000000000009 RBP: 00007ffc5b3caba0 R08: 0000000000000000 R09: 0000000000000037 R10: 000055bee7b8c2a7 R11: 0000000000000246 R12: 000055bee78f1f60 R13: 00007ffc5b3cae90 R14: 0000000000000000 R15: 0000000000000000 </TASK> Modules linked in: bpf_testmod(OE) nls_iso8859_1 dm_multipath scsi_dh_rdac scsi_dh_emc scsi_dh_alua intel_rapl_msr intel_rapl_common intel_uncore_frequency_common ppdev nfit crct10dif_pclmul crc32_pclmul psmouse ghash_clmulni_intel sha512_ssse3 aesni_intel parport_pc crypto_simd cryptd input_leds parport rapl ena i2c_piix4 mac_hid serio_raw ramoops reed_solomon pstore_blk drm pstore_zone efi_pstore autofs4 [last unloaded: bpf_testmod(OE)] CR2: 000000000000000cThough there may be some variation, depending on which suprogram triggers the bug.
Signed-off-by: Krister Johansen kjlx@templeofstupid.com
Acked-by: Yonghong Song yhs@fb.com
linux-kselftest-mirror@lists.linaro.org
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Krister Johansen -
Yonghong Song