On Tue, Mar 24, 2020 at 10:40:55AM -0700, John Fastabend wrote:

Its possible to have divergent ALU32 and ALU64 bounds when using JMP32
instructins and ALU64 arithmatic operations. Sometimes the clang will
even generate this code. Because the case is a bit tricky lets add
a specific test for it.

Here is  pseudocode asm version to illustrate the idea,

 1 r0 = 0xffffffff00000001;
 2 if w0 > 1 goto %l[fail];
 3 r0 += 1
 5 if w0 > 2 goto %l[fail]
 6 exit

The intent here is the verifier will fail the load if the 32bit bounds
are not tracked correctly through ALU64 op. Similarly we can check the
64bit bounds are correctly zero extended after ALU32 ops.

 1 r0 = 0xffffffff00000001;
 2 w0 += 1
 2 if r0 < 0xffffffff00000001 goto %l[fail];

This should be 3.

+	"bounds check mixed 32bit and 64bit arithmatic. test2",
+	.insns = {
+	BPF_MOV64_IMM(BPF_REG_0, 0),
+	BPF_MOV64_IMM(BPF_REG_1, -1),
+	BPF_ALU64_IMM(BPF_LSH, BPF_REG_1, 32),
+	BPF_ALU64_IMM(BPF_ADD, BPF_REG_1, 1),
+	/* r1 = 0xffffFFFF00000001 */
+	BPF_MOV64_IMM(BPF_REG_2, 3),
+	/* r1 = 0x2 */
+	BPF_ALU32_IMM(BPF_ADD, BPF_REG_1, 1),
+	/* check ALU32 op zero extends 64bit bounds */
+	BPF_JMP_REG(BPF_JGT, BPF_REG_1, BPF_REG_2, 1),
+	BPF_JMP_A(1),
+	/* invalid ldx if bounds are lost above */
+	BPF_LDX_MEM(BPF_DW, BPF_REG_0, BPF_REG_0, -1),
+	BPF_EXIT_INSN(),
+	},
+	.result = ACCEPT
+},