diff mbox series

[bpf,v4,1/2] bpf: ensure main program has an extable

Message ID 9253ce691956f19adc93be7dc4c3a7aabe3db3de.1686345886.git.kjlx@templeofstupid.com (mailing list archive)
State Superseded
Delegated to: BPF
Headers show
Series bpf: fix NULL dereference during extable search | expand

Checks

Context Check Description
bpf/vmtest-bpf-VM_Test-9 success Logs for test_maps on x86_64 with gcc
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netdev/series_format success Posting correctly formatted
netdev/tree_selection success Clearly marked for bpf
netdev/fixes_present success Fixes tag present in non-next series
netdev/header_inline success No static functions without inline keyword in header files
netdev/build_32bit success Errors and warnings before: 20 this patch: 20
netdev/cc_maintainers success CCed 12 of 12 maintainers
netdev/build_clang success Errors and warnings before: 8 this patch: 8
netdev/verify_signedoff success Signed-off-by tag matches author and committer
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netdev/check_selftest success No net selftest shell script
netdev/verify_fixes success Fixes tag looks correct
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bpf/vmtest-bpf-PR success PR summary
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Commit Message

Krister Johansen June 9, 2023, 9:40 p.m. UTC 
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 mbox series

Patch

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);