Commit 3f2ac59c authored by Alexei Starovoitov's avatar Alexei Starovoitov
Browse files

Merge branch 'fix-caching-of-btf-for-kfuncs-in-the-verifier' 

Toke Høiland-Jørgensen says:

====================
Fix caching of BTF for kfuncs in the verifier

When playing around with defining kfuncs in some custom modules, we
noticed that if a BPF program calls two functions with the same
signature in two different modules, the function from the wrong module
may sometimes end up being called. Whether this happens depends on the
order of the calls in the BPF program, which turns out to be due to the
use of sort() inside __find_kfunc_desc_btf() in the verifier code.

This series contains a fix for the issue (first patch), and a selftest
to trigger it (last patch). The middle commit is a small refactor to
expose the module loading helper functions in testing_helpers.c. See the
individual patch descriptions for more details.

Changes in v2:
- Drop patch that refactors module building in selftests (Alexei)
- Get rid of expect_val function argument in selftest (Jiri)
- Collect ACKs
- Link to v1: https://lore.kernel.org/r/20241008-fix-kfunc-btf-caching-for-modules-v1-0-dfefd9aa4318@redhat.com

====================

Link: https://lore.kernel.org/r/20241010-fix-kfunc-btf-caching-for-modules-v2-0-745af6c1af98@redhat.com


Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
parents 60f802e2 f91b2566

kernel/bpf/verifier.c

+7 −1
Original line number Diff line number Diff line
@@ -2750,10 +2750,16 @@ static struct btf *__find_kfunc_desc_btf(struct bpf_verifier_env *env, 
		b->module = mod;

		b->offset = offset;









		/* sort() reorders entries by value, so b may no longer point









		 * to the right entry after this









		 */









		sort(tab->descs, tab->nr_descs, sizeof(tab->descs[0]),









		     kfunc_btf_cmp_by_off, NULL);









	} else {









		btf = b->btf;









	}









	return b->btf;

















	return btf;









}

















void bpf_free_kfunc_btf_tab(struct bpf_kfunc_btf_tab *tab)
































tools/testing/selftests/bpf/Makefile



+19
−1






























Original line number
Diff line number
Diff line







@@ -157,7 +157,8 @@ TEST_GEN_PROGS_EXTENDED = \







	flow_dissector_load test_flow_dissector test_tcp_check_syncookie_user \









	test_lirc_mode2_user xdping test_cpp runqslower bench bpf_testmod.ko \









	xskxceiver xdp_redirect_multi xdp_synproxy veristat xdp_hw_metadata \









	xdp_features bpf_test_no_cfi.ko









	xdp_features bpf_test_no_cfi.ko bpf_test_modorder_x.ko \









	bpf_test_modorder_y.ko



















TEST_GEN_FILES += liburandom_read.so urandom_read sign-file uprobe_multi


















@@ -303,6 +304,19 @@ $(OUTPUT)/bpf_test_no_cfi.ko: $(VMLINUX_BTF) $(RESOLVE_BTFIDS) $(wildcard bpf_te







	$(Q)$(MAKE) $(submake_extras) RESOLVE_BTFIDS=$(RESOLVE_BTFIDS) -C bpf_test_no_cfi









	$(Q)cp bpf_test_no_cfi/bpf_test_no_cfi.ko $@



















$(OUTPUT)/bpf_test_modorder_x.ko: $(VMLINUX_BTF) $(RESOLVE_BTFIDS) $(wildcard bpf_test_modorder_x/Makefile bpf_test_modorder_x/*.[ch])









	$(call msg,MOD,,$@)









	$(Q)$(RM) bpf_test_modorder_x/bpf_test_modorder_x.ko # force re-compilation









	$(Q)$(MAKE) $(submake_extras) RESOLVE_BTFIDS=$(RESOLVE_BTFIDS) -C bpf_test_modorder_x









	$(Q)cp bpf_test_modorder_x/bpf_test_modorder_x.ko $@



















$(OUTPUT)/bpf_test_modorder_y.ko: $(VMLINUX_BTF) $(RESOLVE_BTFIDS) $(wildcard bpf_test_modorder_y/Makefile bpf_test_modorder_y/*.[ch])









	$(call msg,MOD,,$@)









	$(Q)$(RM) bpf_test_modorder_y/bpf_test_modorder_y.ko # force re-compilation









	$(Q)$(MAKE) $(submake_extras) RESOLVE_BTFIDS=$(RESOLVE_BTFIDS) -C bpf_test_modorder_y









	$(Q)cp bpf_test_modorder_y/bpf_test_modorder_y.ko $@





























DEFAULT_BPFTOOL := $(HOST_SCRATCH_DIR)/sbin/bpftool









ifneq ($(CROSS_COMPILE),)









CROSS_BPFTOOL := $(SCRATCH_DIR)/sbin/bpftool








@@ -722,6 +736,8 @@ TRUNNER_EXTRA_SOURCES := test_progs.c		\







			 ip_check_defrag_frags.h









TRUNNER_EXTRA_FILES := $(OUTPUT)/urandom_read $(OUTPUT)/bpf_testmod.ko	\









		       $(OUTPUT)/bpf_test_no_cfi.ko			\









		       $(OUTPUT)/bpf_test_modorder_x.ko		\









		       $(OUTPUT)/bpf_test_modorder_y.ko		\









		       $(OUTPUT)/liburandom_read.so			\









		       $(OUTPUT)/xdp_synproxy				\









		       $(OUTPUT)/sign-file				\








@@ -856,6 +872,8 @@ EXTRA_CLEAN := $(SCRATCH_DIR) $(HOST_SCRATCH_DIR)			\







	$(addprefix $(OUTPUT)/,*.o *.d *.skel.h *.lskel.h *.subskel.h	\









			       no_alu32 cpuv4 bpf_gcc bpf_testmod.ko	\









			       bpf_test_no_cfi.ko			\









			       bpf_test_modorder_x.ko			\









			       bpf_test_modorder_y.ko			\









			       liburandom_read.so)			\









	$(OUTPUT)/FEATURE-DUMP.selftests










































tools/testing/selftests/bpf/bpf_test_modorder_x/Makefile
0 → 100644



+19
−0






























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Diff line number
Diff line









BPF_TESTMOD_DIR := $(realpath $(dir $(abspath $(lastword $(MAKEFILE_LIST)))))









KDIR ?= $(abspath $(BPF_TESTMOD_DIR)/../../../../..)



















ifeq ($(V),1)









Q =









else









Q = @









endif



















MODULES = bpf_test_modorder_x.ko



















obj-m += bpf_test_modorder_x.o



















all:









	+$(Q)make -C $(KDIR) M=$(BPF_TESTMOD_DIR) modules



















clean:









	+$(Q)make -C $(KDIR) M=$(BPF_TESTMOD_DIR) clean

































tools/testing/selftests/bpf/bpf_test_modorder_x/bpf_test_modorder_x.c
0 → 100644



+39
−0






























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Diff line number
Diff line









// SPDX-License-Identifier: GPL-2.0









#include <linux/bpf.h>









#include <linux/btf.h>









#include <linux/module.h>









#include <linux/init.h>



















__bpf_kfunc_start_defs();



















__bpf_kfunc int bpf_test_modorder_retx(void)









{









	return 'x';









}



















__bpf_kfunc_end_defs();



















BTF_KFUNCS_START(bpf_test_modorder_kfunc_x_ids)









BTF_ID_FLAGS(func, bpf_test_modorder_retx);









BTF_KFUNCS_END(bpf_test_modorder_kfunc_x_ids)



















static const struct btf_kfunc_id_set bpf_test_modorder_x_set = {









	.owner = THIS_MODULE,









	.set = &bpf_test_modorder_kfunc_x_ids,









};



















static int __init bpf_test_modorder_x_init(void)









{









	return register_btf_kfunc_id_set(BPF_PROG_TYPE_SCHED_CLS,









					 &bpf_test_modorder_x_set);









}



















static void __exit bpf_test_modorder_x_exit(void)









{









}



















module_init(bpf_test_modorder_x_init);









module_exit(bpf_test_modorder_x_exit);



















MODULE_DESCRIPTION("BPF selftest ordertest module X");









MODULE_LICENSE("GPL");
























tools/testing/selftests/bpf/bpf_test_modorder_y/Makefile
0 → 100644



+19
−0






























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Diff line number
Diff line









BPF_TESTMOD_DIR := $(realpath $(dir $(abspath $(lastword $(MAKEFILE_LIST)))))









KDIR ?= $(abspath $(BPF_TESTMOD_DIR)/../../../../..)



















ifeq ($(V),1)









Q =









else









Q = @









endif



















MODULES = bpf_test_modorder_y.ko



















obj-m += bpf_test_modorder_y.o



















all:









	+$(Q)make -C $(KDIR) M=$(BPF_TESTMOD_DIR) modules



















clean:









	+$(Q)make -C $(KDIR) M=$(BPF_TESTMOD_DIR) clean