netdev - [bpf-next PATCH 09/10] bpf: test_verifier, #65 error message updates for trunc of boundary-cross

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Date:   Tue, 24 Mar 2020 10:40:36 -0700
From:   John Fastabend <john.fastabend@...il.com>
To:     ecree@...arflare.com, yhs@...com, alexei.starovoitov@...il.com,
        daniel@...earbox.net
Cc:     netdev@...r.kernel.org, bpf@...r.kernel.org,
        john.fastabend@...il.com
Subject: [bpf-next PATCH 09/10] bpf: test_verifier,
 #65 error message updates for trunc of boundary-cross

After changes to add update_reg_bounds after ALU ops and 32-bit bounds
tracking truncation of boundary crossing range will fail earlier and with
a different error message. Now the test error trace is the following

11: (17) r1 -= 2147483584
12: R0_w=map_value(id=0,off=0,ks=8,vs=8,imm=0)
    R1_w=invP(id=0,smin_value=-2147483584,smax_value=63)
    R10=fp0 fp-8_w=mmmmmmmm
12: (17) r1 -= 2147483584
13: R0_w=map_value(id=0,off=0,ks=8,vs=8,imm=0)
    R1_w=invP(id=0,
              umin_value=18446744069414584448,umax_value=18446744071562068095,
              var_off=(0xffffffff00000000; 0xffffffff))
    R10=fp0 fp-8_w=mmmmmmmm
13: (77) r1 >>= 8
14: R0_w=map_value(id=0,off=0,ks=8,vs=8,imm=0)
    R1_w=invP(id=0,
              umin_value=72057594021150720,umax_value=72057594029539328,
              var_off=(0xffffffff000000; 0xffffff),
              s32_min_value=-16777216,s32_max_value=-1,
              u32_min_value=-16777216)
    R10=fp0 fp-8_w=mmmmmmmm
14: (0f) r0 += r1
value 72057594021150720 makes map_value pointer be out of bounds

Because we have 'umin_value == umax_value' instead of previously
where 'umin_value != umax_value' we can now fail earlier noting
that pointer addition is out of bounds.

Signed-off-by: John Fastabend <john.fastabend@...il.com>
---
 tools/testing/selftests/bpf/verifier/bounds.c |   12 ++++--------
 1 file changed, 4 insertions(+), 8 deletions(-)

diff --git a/tools/testing/selftests/bpf/verifier/bounds.c b/tools/testing/selftests/bpf/verifier/bounds.c
index 7c9b659..cf72fcc 100644
--- a/tools/testing/selftests/bpf/verifier/bounds.c
+++ b/tools/testing/selftests/bpf/verifier/bounds.c
@@ -257,17 +257,15 @@
 	 *      [0x00ff'ffff'ff00'0000, 0x00ff'ffff'ffff'ffff]
 	 */
 	BPF_ALU64_IMM(BPF_RSH, BPF_REG_1, 8),
-	/* no-op or OOB pointer computation */
+	/* error on OOB pointer computation */
 	BPF_ALU64_REG(BPF_ADD, BPF_REG_0, BPF_REG_1),
-	/* potentially OOB access */
-	BPF_LDX_MEM(BPF_B, BPF_REG_0, BPF_REG_0, 0),
 	/* exit */
 	BPF_MOV64_IMM(BPF_REG_0, 0),
 	BPF_EXIT_INSN(),
 	},
 	.fixup_map_hash_8b = { 3 },
 	/* not actually fully unbounded, but the bound is very high */
-	.errstr = "R0 unbounded memory access",
+	.errstr = "value 72057594021150720 makes map_value pointer be out of bounds",
 	.result = REJECT
 },
 {
@@ -299,17 +297,15 @@
 	 *      [0x00ff'ffff'ff00'0000, 0x00ff'ffff'ffff'ffff]
 	 */
 	BPF_ALU64_IMM(BPF_RSH, BPF_REG_1, 8),
-	/* no-op or OOB pointer computation */
+	/* error on OOB pointer computation */
 	BPF_ALU64_REG(BPF_ADD, BPF_REG_0, BPF_REG_1),
-	/* potentially OOB access */
-	BPF_LDX_MEM(BPF_B, BPF_REG_0, BPF_REG_0, 0),
 	/* exit */
 	BPF_MOV64_IMM(BPF_REG_0, 0),
 	BPF_EXIT_INSN(),
 	},
 	.fixup_map_hash_8b = { 3 },
 	/* not actually fully unbounded, but the bound is very high */
-	.errstr = "R0 unbounded memory access",
+	.errstr = "value 72057594021150720 makes map_value pointer be out of bounds",
 	.result = REJECT
 },
 {