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[PATCHv4,bpf-next,01/10] libbpf: Store zero fd to fd_array for loader kfunc relocation

Message ID 20230515133756.1658301-2-jolsa@kernel.org (mailing list archive)
State Accepted
Commit 10cb8622b6958c2d47961d6a42c76e6c9f1c08f3
Delegated to: BPF
Headers show
Series bpf: Move kernel test kfuncs into bpf_testmod | expand

Checks

Context Check Description
bpf/vmtest-bpf-next-VM_Test-10 fail Logs for test_maps on s390x with gcc
netdev/series_format success Posting correctly formatted
netdev/tree_selection success Clearly marked for bpf-next, async
netdev/fixes_present success Fixes tag not required for -next series
netdev/header_inline success No static functions without inline keyword in header files
netdev/build_32bit success Errors and warnings before: 8 this patch: 8
netdev/cc_maintainers warning 3 maintainers not CCed: kpsingh@kernel.org martin.lau@linux.dev song@kernel.org
netdev/build_clang success Errors and warnings before: 8 this patch: 8
netdev/verify_signedoff success Signed-off-by tag matches author and committer
netdev/deprecated_api success None detected
netdev/check_selftest success No net selftest shell script
netdev/verify_fixes success No Fixes tag
netdev/build_allmodconfig_warn success Errors and warnings before: 8 this patch: 8
netdev/checkpatch warning WARNING: line length of 83 exceeds 80 columns
netdev/kdoc success Errors and warnings before: 0 this patch: 0
netdev/source_inline success Was 0 now: 0
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bpf/vmtest-bpf-next-VM_Test-33 success Logs for test_verifier on s390x with gcc
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bpf/vmtest-bpf-next-VM_Test-15 success Logs for test_progs on s390x with gcc
bpf/vmtest-bpf-next-PR success PR summary
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Commit Message

Jiri Olsa May 15, 2023, 1:37 p.m. UTC 
When moving some of the test kfuncs to bpf_testmod I hit an issue
when some of the kfuncs that object uses are in module and some
in vmlinux.

The problem is that both vmlinux and module kfuncs get allocated
btf_fd_idx index into fd_array, but we store to it the BTF fd value
only for module's kfunc, not vmlinux's one because (it's zero).

Then after the program is loaded we check if fd_array[btf_fd_idx] != 0
and close the fd.

When the object has kfuncs from both vmlinux and module, the fd from
fd_array[btf_fd_idx] from previous load will be stored in there for
vmlinux's kfunc, so we close unrelated fd (of the program we just
loaded in my case).

Fixing this by storing zero to fd_array[btf_fd_idx] for vmlinux
kfuncs, so the we won't close stale fd.

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
---
 tools/lib/bpf/gen_loader.c | 14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)
diff mbox series

Patch

diff --git a/tools/lib/bpf/gen_loader.c b/tools/lib/bpf/gen_loader.c
index 83e8e3bfd8ff..cf3323fd47b8 100644
--- a/tools/lib/bpf/gen_loader.c
+++ b/tools/lib/bpf/gen_loader.c
@@ -703,17 +703,17 @@  static void emit_relo_kfunc_btf(struct bpf_gen *gen, struct ksym_relo_desc *relo
 	/* obtain fd in BPF_REG_9 */
 	emit(gen, BPF_MOV64_REG(BPF_REG_9, BPF_REG_7));
 	emit(gen, BPF_ALU64_IMM(BPF_RSH, BPF_REG_9, 32));
-	/* jump to fd_array store if fd denotes module BTF */
-	emit(gen, BPF_JMP_IMM(BPF_JNE, BPF_REG_9, 0, 2));
-	/* set the default value for off */
-	emit(gen, BPF_ST_MEM(BPF_H, BPF_REG_8, offsetof(struct bpf_insn, off), 0));
-	/* skip BTF fd store for vmlinux BTF */
-	emit(gen, BPF_JMP_IMM(BPF_JA, 0, 0, 4));
 	/* load fd_array slot pointer */
 	emit2(gen, BPF_LD_IMM64_RAW_FULL(BPF_REG_0, BPF_PSEUDO_MAP_IDX_VALUE,
 					 0, 0, 0, blob_fd_array_off(gen, btf_fd_idx)));
-	/* store BTF fd in slot */
+	/* store BTF fd in slot, 0 for vmlinux */
 	emit(gen, BPF_STX_MEM(BPF_W, BPF_REG_0, BPF_REG_9, 0));
+	/* jump to insn[insn_idx].off store if fd denotes module BTF */
+	emit(gen, BPF_JMP_IMM(BPF_JNE, BPF_REG_9, 0, 2));
+	/* set the default value for off */
+	emit(gen, BPF_ST_MEM(BPF_H, BPF_REG_8, offsetof(struct bpf_insn, off), 0));
+	/* skip BTF fd store for vmlinux BTF */
+	emit(gen, BPF_JMP_IMM(BPF_JA, 0, 0, 1));
 	/* store index into insn[insn_idx].off */
 	emit(gen, BPF_ST_MEM(BPF_H, BPF_REG_8, offsetof(struct bpf_insn, off), btf_fd_idx));
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