linux-kernel - [PATCH bpf-next v2 09/11] selftests/bpf: Add test for Spectre v1 mitigation

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Message-ID: <20250421091802.3234859-10-luis.gerhorst@fau.de>
Date: Mon, 21 Apr 2025 11:18:00 +0200
From: Luis Gerhorst <luis.gerhorst@....de>
To: Alexei Starovoitov <ast@...nel.org>,
	Daniel Borkmann <daniel@...earbox.net>,
	Andrii Nakryiko <andrii@...nel.org>,
	Martin KaFai Lau <martin.lau@...ux.dev>,
	Eduard Zingerman <eddyz87@...il.com>,
	Song Liu <song@...nel.org>,
	Yonghong Song <yonghong.song@...ux.dev>,
	John Fastabend <john.fastabend@...il.com>,
	KP Singh <kpsingh@...nel.org>,
	Stanislav Fomichev <sdf@...ichev.me>,
	Hao Luo <haoluo@...gle.com>,
	Jiri Olsa <jolsa@...nel.org>,
	Puranjay Mohan <puranjay@...nel.org>,
	Xu Kuohai <xukuohai@...weicloud.com>,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will@...nel.org>,
	Hari Bathini <hbathini@...ux.ibm.com>,
	Christophe Leroy <christophe.leroy@...roup.eu>,
	Naveen N Rao <naveen@...nel.org>,
	Madhavan Srinivasan <maddy@...ux.ibm.com>,
	Michael Ellerman <mpe@...erman.id.au>,
	Nicholas Piggin <npiggin@...il.com>,
	Mykola Lysenko <mykolal@...com>,
	Shuah Khan <shuah@...nel.org>,
	Luis Gerhorst <luis.gerhorst@....de>,
	Henriette Herzog <henriette.herzog@....de>,
	Saket Kumar Bhaskar <skb99@...ux.ibm.com>,
	Cupertino Miranda <cupertino.miranda@...cle.com>,
	Jiayuan Chen <mrpre@....com>,
	Matan Shachnai <m.shachnai@...il.com>,
	Dimitar Kanaliev <dimitar.kanaliev@...eground.com>,
	Shung-Hsi Yu <shung-hsi.yu@...e.com>,
	Daniel Xu <dxu@...uu.xyz>,
	bpf@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org,
	linuxppc-dev@...ts.ozlabs.org,
	linux-kselftest@...r.kernel.org
Subject: [PATCH bpf-next v2 09/11] selftests/bpf: Add test for Spectre v1 mitigation

This is based on the gadget from the description of commit 9183671af6db
("bpf: Fix leakage under speculation on mispredicted branches").

Signed-off-by: Luis Gerhorst <luis.gerhorst@....de>
---
 .../selftests/bpf/progs/verifier_unpriv.c     | 57 +++++++++++++++++++
 1 file changed, 57 insertions(+)

diff --git a/tools/testing/selftests/bpf/progs/verifier_unpriv.c b/tools/testing/selftests/bpf/progs/verifier_unpriv.c
index c42c3839b30c..43236b93ebb5 100644
--- a/tools/testing/selftests/bpf/progs/verifier_unpriv.c
+++ b/tools/testing/selftests/bpf/progs/verifier_unpriv.c
@@ -729,4 +729,61 @@ l0_%=:	r0 = 0;						\
 "	::: __clobber_all);
 }
 
+SEC("socket")
+__description("unpriv: Spectre v1 path-based type confusion of scalar as stack-ptr")
+__success __success_unpriv __retval(0)
+#ifdef SPEC_V1
+__xlated_unpriv("if r0 != 0x1 goto pc+2")
+/* This nospec prevents the exploit because it forces the mispredicted (not
+ * taken) `if r0 != 0x0 goto l0_%=` to resolve before using r6 as a pointer.
+ * This causes the CPU to realize that `r6 = r9` should have never executed. It
+ * ensures that r6 always contains a readable stack slot ptr when the insn after
+ * the nospec executes.
+ */
+__xlated_unpriv("nospec")
+__xlated_unpriv("r9 = *(u8 *)(r6 +0)")
+#endif
+__naked void unpriv_spec_v1_type_confusion(void)
+{
+	asm volatile ("					\
+	r1 = 0;						\
+	*(u64*)(r10 - 8) = r1;				\
+	r2 = r10;					\
+	r2 += -8;					\
+	r1 = %[map_hash_8b] ll;				\
+	call %[bpf_map_lookup_elem];			\
+	if r0 == 0 goto l2_%=;				\
+	/* r0: pointer to a map array entry */		\
+	r2 = r10;					\
+	r2 += -8;					\
+	r1 = %[map_hash_8b] ll;				\
+	/* r1, r2: prepared call args */		\
+	r6 = r10;					\
+	r6 += -8;					\
+	/* r6: pointer to readable stack slot */	\
+	r9 = 0xffffc900;				\
+	r9 <<= 32;					\
+	/* r9: scalar controlled by attacker */		\
+	r0 = *(u64 *)(r0 + 0); /* cache miss */		\
+	if r0 != 0x0 goto l0_%=;			\
+	r6 = r9;					\
+l0_%=:	if r0 != 0x1 goto l1_%=;			\
+	r9 = *(u8 *)(r6 + 0);				\
+l1_%=:  /* leak r9 */					\
+	r9 &= 1;					\
+	r9 <<= 9;					\
+	*(u64*)(r10 - 8) = r9;				\
+	call %[bpf_map_lookup_elem];			\
+	if r0 == 0 goto l2_%=;				\
+	/* leak secret into is_cached(map[0|512]): */	\
+	r0 = *(u64 *)(r0 + 0);				\
+l2_%=:							\
+	r0 = 0;						\
+	exit;						\
+"	:
+	: __imm(bpf_map_lookup_elem),
+	  __imm_addr(map_hash_8b)
+	: __clobber_all);
+}
+
 char _license[] SEC("license") = "GPL";
-- 
2.49.0