selftests/bpf: Add Spectre v4 tests

Add the following tests:

1. A test with an (unimportant) ldimm64 (16 byte insn) and a
   Spectre-v4--induced nospec that clarifies and serves as a basic
   Spectre v4 test.

2. Make sure a Spectre v4 nospec_result does not prevent a Spectre v1
   nospec from being added before the dangerous instruction (tests that
   [1] is fixed).

3. Combine the two, which is the combination that triggers the warning
   in [2]. This is because the unanalyzed stack write has nospec_result
   set, but the ldimm64 (which was just analyzed) had incremented
   insn_idx by 2. That violates the assertion that nospec_result is only
   used after insns that increment insn_idx by 1 (i.e., stack writes).

[1] https://lore.kernel.org/bpf/4266fd5de04092aa4971cbef14f1b4b96961f432.camel@gmail.com/
[2] https://lore.kernel.org/bpf/685b3c1b.050a0220.2303ee.0010.GAE@google.com/

Signed-off-by: Luis Gerhorst <luis.gerhorst@fau.de>

Author: luisgerhorst

tools/testing/selftests/bpf/progs/bpf_misc.h

@@ -237,4 +237,8 @@
 #define SPEC_V1
 #endif
 
+#if defined(__TARGET_ARCH_x86)
+#define SPEC_V4
+#endif
+
 #endif

tools/testing/selftests/bpf/progs/verifier_unpriv.c

@@ -801,4 +801,153 @@ l2_%=:							\
 	: __clobber_all);
 }
 
+SEC("socket")
+__description("unpriv: ldimm64 before Spectre v4 barrier")
+__success __success_unpriv
+__retval(0)
+#ifdef SPEC_V4
+__xlated_unpriv("r1 = 0x2020200005642020") /* should not matter */
+__xlated_unpriv("*(u64 *)(r10 -8) = r1")
+__xlated_unpriv("nospec")
+#endif
+__naked void unpriv_ldimm64_spectre_v4(void)
+{
+	asm volatile ("					\
+	r1 = 0x2020200005642020 ll;			\
+	*(u64 *)(r10 -8) = r1;				\
+	r0 = 0;						\
+	exit;						\
+"	::: __clobber_all);
+}
+
+SEC("socket")
+__description("unpriv: Spectre v1 and v4 barrier")
+__success __success_unpriv
+__retval(0)
+#ifdef SPEC_V1
+#ifdef SPEC_V4
+/* starts with r0 == r8 == r9 == 0 */
+__xlated_unpriv("if r8 != 0x0 goto pc+1")
+__xlated_unpriv("goto pc+2")
+__xlated_unpriv("if r9 == 0x0 goto pc+4")
+__xlated_unpriv("r2 = r0")
+/* Following nospec required to prevent following dangerous `*(u64 *)(NOT_FP -64)
+ * = r1` iff `if r9 == 0 goto pc+4` was mispredicted because of Spectre v1. The
+ * test therefore ensures the Spectre-v4--induced nospec does not prevent the
+ * Spectre-v1--induced speculative path from being fully analyzed.
+ */
+__xlated_unpriv("nospec") /* Spectre v1 */
+__xlated_unpriv("*(u64 *)(r2 -64) = r1") /* could be used to leak r2 */
+__xlated_unpriv("nospec") /* Spectre v4 */
+#endif
+#endif
+__naked void unpriv_spectre_v1_and_v4(void)
+{
+	asm volatile ("					\
+	r1 = 0;						\
+	*(u64*)(r10 - 8) = r1;				\
+	r2 = r10;					\
+	r2 += -8;					\
+	r1 = %[map_hash_8b] ll;				\
+	call %[bpf_map_lookup_elem];			\
+	r8 = r0;					\
+	r2 = r10;					\
+	r2 += -8;					\
+	r1 = %[map_hash_8b] ll;				\
+	call %[bpf_map_lookup_elem];			\
+	r9 = r0;					\
+	r0 = r10;					\
+	r1 = 0;						\
+	r2 = r10;					\
+	if r8 != 0 goto l0_%=;				\
+	if r9 != 0 goto l0_%=;				\
+	r0 = 0;						\
+l0_%=:	if r8 != 0 goto l1_%=;				\
+	goto l2_%=;					\
+l1_%=:	if r9 == 0 goto l3_%=;				\
+	r2 = r0;					\
+l2_%=:	*(u64 *)(r2 -64) = r1;				\
+l3_%=:	r0 = 0;						\
+	exit;						\
+"	:
+	: __imm(bpf_map_lookup_elem),
+	  __imm_addr(map_hash_8b)
+	: __clobber_all);
+}
+
+SEC("socket")
+__description("unpriv: Spectre v1 and v4 barrier (simple)")
+__success __success_unpriv
+__retval(0)
+#ifdef SPEC_V1
+#ifdef SPEC_V4
+__xlated_unpriv("if r8 != 0x0 goto pc+1")
+__xlated_unpriv("goto pc+2")
+__xlated_unpriv("goto pc-1") /* if r9 == 0 goto l3_%= */
+__xlated_unpriv("goto pc-1") /* r2 = r0 */
+__xlated_unpriv("nospec")
+__xlated_unpriv("*(u64 *)(r2 -64) = r1")
+__xlated_unpriv("nospec")
+#endif
+#endif
+__naked void unpriv_spectre_v1_and_v4_simple(void)
+{
+	asm volatile ("					\
+	r8 = 0;						\
+	r9 = 0;						\
+	r0 = r10;					\
+	r1 = 0;						\
+	r2 = r10;					\
+	if r8 != 0 goto l0_%=;				\
+	if r9 != 0 goto l0_%=;				\
+	r0 = 0;						\
+l0_%=:	if r8 != 0 goto l1_%=;				\
+	goto l2_%=;					\
+l1_%=:	if r9 == 0 goto l3_%=;				\
+	r2 = r0;					\
+l2_%=:	*(u64 *)(r2 -64) = r1;				\
+l3_%=:	r0 = 0;						\
+	exit;						\
+"	::: __clobber_all);
+}
+
+SEC("socket")
+__description("unpriv: ldimm64 before Spectre v1 and v4 barrier (simple)")
+__success __success_unpriv
+__retval(0)
+#ifdef SPEC_V1
+#ifdef SPEC_V4
+__xlated_unpriv("if r8 != 0x0 goto pc+1")
+__xlated_unpriv("goto pc+4")
+__xlated_unpriv("goto pc-1") /* if r9 == 0 goto l3_%= */
+__xlated_unpriv("goto pc-1") /* r2 = r0 */
+__xlated_unpriv("goto pc-1") /* r1 = 0x2020200005642020 ll */
+__xlated_unpriv("goto pc-1") /* second part of ldimm64 */
+__xlated_unpriv("nospec")
+__xlated_unpriv("*(u64 *)(r2 -64) = r1")
+__xlated_unpriv("nospec")
+#endif
+#endif
+__naked void unpriv_ldimm64_spectre_v1_and_v4_simple(void)
+{
+	asm volatile ("					\
+	r8 = 0;						\
+	r9 = 0;						\
+	r0 = r10;					\
+	r1 = 0;						\
+	r2 = r10;					\
+	if r8 != 0 goto l0_%=;				\
+	if r9 != 0 goto l0_%=;				\
+	r0 = 0;						\
+l0_%=:	if r8 != 0 goto l1_%=;				\
+	goto l2_%=;					\
+l1_%=:	if r9 == 0 goto l3_%=;				\
+	r2 = r0;					\
+	r1 = 0x2020200005642020 ll;			\
+l2_%=:	*(u64 *)(r2 -64) = r1;				\
+l3_%=:	r0 = 0;						\
+	exit;						\
+"	::: __clobber_all);
+}
+
 char _license[] SEC("license") = "GPL";