[PATCH bpf-next v2 21/22] selftests/bpf: Test jumps around patches of bpf_do_misc_fixups()

[Qiliang Yuan]

bpf_do_misc_fixups() queues its patches and applies them at once,
relocating every jump through a map from old to new indices.

No test checks the xlated code of jumps that target, skip or leave such
patches, a jump that the patches push out of its 16-bit range, or an
indirect jump to a patched instruction.

Check the xlated code for forward and backward jumps to a patched
instruction, jumps over patches, and a may_goto whose jump leaves its
own patch and crosses another one. Check that a jump over 8200 guarded
divisions fails to load, and that a gotox to a guarded modulo by zero
lands on the guard.

Signed-off-by: Qiliang Yuan <odys.yuan@xxxxxxxxx>
---
 tools/testing/selftests/bpf/prog_tests/verifier.c  |   2 +
 .../selftests/bpf/progs/verifier_patch_list.c      | 175 +++++++++++++++++++++
 2 files changed, 177 insertions(+)

diff --git a/tools/testing/selftests/bpf/prog_tests/verifier.c b/tools/testing/selftests/bpf/prog_tests/verifier.c
index 04740ba37e918..40788891641b5 100644
--- a/tools/testing/selftests/bpf/prog_tests/verifier.c
+++ b/tools/testing/selftests/bpf/prog_tests/verifier.c
@@ -96,6 +96,7 @@
 #include "verifier_netfilter_retcode.skel.h"
 #include "verifier_bpf_fastcall.skel.h"
 #include "verifier_or_jmp32_k.skel.h"
+#include "verifier_patch_list.skel.h"
 #include "verifier_percpu_addr.skel.h"
 #include "verifier_precision.skel.h"
 #include "verifier_prevent_map_lookup.skel.h"
@@ -287,6 +288,7 @@ void test_verifier_netfilter_ctx(void)        { RUN(verifier_netfilter_ctx); }
 void test_verifier_netfilter_retcode(void)    { RUN(verifier_netfilter_retcode); }
 void test_verifier_bpf_fastcall(void)         { RUN(verifier_bpf_fastcall); }
 void test_verifier_or_jmp32_k(void)           { RUN(verifier_or_jmp32_k); }
+void test_verifier_patch_list(void)           { RUN(verifier_patch_list); }
 void test_verifier_percpu_addr(void)          { RUN(verifier_percpu_addr); }
 void test_verifier_precision(void)            { RUN(verifier_precision); }
 void test_verifier_prevent_map_lookup(void)   { RUN(verifier_prevent_map_lookup); }
diff --git a/tools/testing/selftests/bpf/progs/verifier_patch_list.c b/tools/testing/selftests/bpf/progs/verifier_patch_list.c
new file mode 100644
index 0000000000000..1370cdd5e5836
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/verifier_patch_list.c
@@ -0,0 +1,175 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/bpf.h>
+#include <bpf/bpf_helpers.h>
+#include "../../../include/linux/filter.h"
+#include "bpf_misc.h"
+
+/*
+ * bpf_do_misc_fixups() guards each division by a register against division
+ * by zero with a 4 insn patch. Jumps to a patched insn must land on the
+ * first insn of its patch, other jumps must follow the insns they target.
+ */
+
+SEC("raw_tp")
+__description("patch list: forward jumps to and over patched insns")
+__arch_x86_64
+__arch_arm64
+__success
+__xlated("0: call")
+__xlated("1: r1 = r0")
+__xlated("2: r0 = 7")
+__xlated("3: if r1 > 0x5 goto pc+1")
+__xlated("4: r0 = 9")
+__xlated("5: if r1 != 0x0 goto pc+2")
+__xlated("6: w0 ^= w0")
+__xlated("7: goto pc+1")
+__xlated("8: r0 /= r1")
+__xlated("9: if r0 > 0x3 goto pc+4")
+__xlated("10: if r1 != 0x0 goto pc+2")
+__xlated("11: w0 ^= w0")
+__xlated("12: goto pc+1")
+__xlated("13: r0 /= r1")
+__xlated("14: exit")
+__naked void patch_list_forward(void)
+{
+	asm volatile (
+	"call %[bpf_get_prandom_u32];"
+	"r1 = r0;"
+	"r0 = 7;"
+	"if r1 > 5 goto l0_%=;"
+	"r0 = 9;"
+"l0_%=:"
+	"r0 /= r1;"
+	"if r0 > 3 goto l1_%=;"
+	"r0 /= r1;"
+"l1_%=:"
+	"exit;"
+	:
+	: __imm(bpf_get_prandom_u32)
+	: __clobber_all);
+}
+
+SEC("raw_tp")
+__description("patch list: backward jump to a patched insn")
+__arch_x86_64
+__arch_arm64
+__success
+__xlated("0: call")
+__xlated("1: r1 = r0")
+__xlated("2: r2 = 0")
+__xlated("3: if r1 != 0x0 goto pc+2")
+__xlated("4: w0 ^= w0")
+__xlated("5: goto pc+1")
+__xlated("6: r0 /= r1")
+__xlated("7: r2 += 1")
+__xlated("8: if r2 < 0x3 goto pc-6")
+__xlated("9: exit")
+__naked void patch_list_backward(void)
+{
+	asm volatile (
+	"call %[bpf_get_prandom_u32];"
+	"r1 = r0;"
+	"r2 = 0;"
+"l0_%=:"
+	"r0 /= r1;"
+	"r2 += 1;"
+	"if r2 < 3 goto l0_%=;"
+	"exit;"
+	:
+	: __imm(bpf_get_prandom_u32)
+	: __clobber_all);
+}
+
+/* The jump of may_goto leaves its own patch and crosses another one. */
+SEC("raw_tp")
+__description("patch list: may_goto between patched insns")
+__arch_x86_64
+__success
+__xlated("0: *(u64 *)(r10 -16) = 65535")
+__xlated("1: *(u64 *)(r10 -8) = 0")
+__xlated("2: call")
+__xlated("3: r1 = r0")
+__xlated("4: if r1 != 0x0 goto pc+2")
+__xlated("5: w0 ^= w0")
+__xlated("6: goto pc+1")
+__xlated("7: r0 /= r1")
+__xlated("8: r12 = *(u64 *)(r10 -16)")
+__xlated("9: if r12 == 0x0 goto pc+9")
+__xlated("...")
+__xlated("15: if r1 != 0x0 goto pc+2")
+__xlated("16: w0 ^= w0")
+__xlated("17: goto pc+1")
+__xlated("18: r0 /= r1")
+__xlated("19: exit")
+__naked void patch_list_may_goto(void)
+{
+	asm volatile (
+	"call %[bpf_get_prandom_u32];"
+	"r1 = r0;"
+	"r0 /= r1;"
+	".8byte %[may_goto];"
+	"r0 /= r1;"
+	"exit;"
+	:
+	: __imm(bpf_get_prandom_u32),
+	  __imm_insn(may_goto, BPF_RAW_INSN(BPF_JMP | BPF_JCOND, 0, 0, 1 /* offset */, 0))
+	: __clobber_all);
+}
+
+/*
+ * The conditional jump skips 8200 divisions, which their patches turn into
+ * 32800 insns, too far for its 16-bit offset.
+ */
+SEC("raw_tp")
+__description("patch list: jump pushed out of range by patches")
+__failure __msg("cannot be patched due to 16-bit range")
+__naked void patch_list_jump_out_of_range(void)
+{
+	asm volatile ("					\
+	call %[bpf_get_prandom_u32];			\
+	r1 = r0;					\
+	if r0 == 0 goto 0f;				\
+	.rept 8200;					\
+	r0 /= r1;					\
+	.endr;						\
+0:	r0 = 0;						\
+	exit;						\
+"	:
+	: __imm(bpf_get_prandom_u32)
+	: __clobber_all);
+}
+
+#if defined(__TARGET_ARCH_x86) || defined(__TARGET_ARCH_arm64) || defined(__TARGET_ARCH_powerpc)
+/*
+ * An indirect jump to a patched insn must land on the first insn of its
+ * patch, here the check that skips the modulo by zero.
+ */
+SEC("socket")
+__description("patch list: indirect jump to a patched insn")
+__success __retval(7)
+__naked void patch_list_indirect(void)
+{
+	asm volatile ("					\
+	.pushsection .jumptables,\"\",@progbits;	\
+jt0_%=:							\
+	.quad l0_%= - socket;				\
+	.size jt0_%=, 8;				\
+	.global jt0_%=;					\
+	.popsection;					\
+	r1 = 0;						\
+	r6 = 7;						\
+	r0 = jt0_%= ll;					\
+	r0 = *(u64 *)(r0 + 0);				\
+	.8byte %[gotox_r0];				\
+l0_%=:							\
+	r6 %%= r1;					\
+	r0 = r6;					\
+	exit;						\
+"	:
+	: __imm_insn(gotox_r0, BPF_RAW_INSN(BPF_JMP | BPF_JA | BPF_X, BPF_REG_0, 0, 0, 0))
+	: __clobber_all);
+}
+#endif
+
+char _license[] SEC("license") = "GPL";

-- 
2.43.0