samples/seccomp: fix 64-bit comparison macros

There were some bugs in the JNE64 and JLT64 comparision macros. This fixes
them, improves comments, and cleans up the file while we are at it.
Reported-by: Stephen Röttger <sroettger@google.com>
Signed-off-by: Mathias Svensson <idolf@google.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
Cc: stable@vger.kernel.org
Signed-off-by: James Morris <james.l.morris@oracle.com>

samples/seccomp/bpf-helper.h

@@ -138,7 +138,7 @@ union arg64 {
 #define ARG_32(idx) \
 	BPF_STMT(BPF_LD+BPF_W+BPF_ABS, LO_ARG(idx))
 
-/* Loads hi into A and lo in X */
+/* Loads lo into M[0] and hi into M[1] and A */
 #define ARG_64(idx) \
 	BPF_STMT(BPF_LD+BPF_W+BPF_ABS, LO_ARG(idx)), \
 	BPF_STMT(BPF_ST, 0), /* lo -> M[0] */ \
@@ -153,88 +153,107 @@ union arg64 {
 	BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, (value), 1, 0), \
 	jt
 
-/* Checks the lo, then swaps to check the hi. A=lo,X=hi */
+#define JA32(value, jt) \
+	BPF_JUMP(BPF_JMP+BPF_JSET+BPF_K, (value), 0, 1), \
+	jt
+
+#define JGE32(value, jt) \
+	BPF_JUMP(BPF_JMP+BPF_JGE+BPF_K, (value), 0, 1), \
+	jt
+
+#define JGT32(value, jt) \
+	BPF_JUMP(BPF_JMP+BPF_JGT+BPF_K, (value), 0, 1), \
+	jt
+
+#define JLE32(value, jt) \
+	BPF_JUMP(BPF_JMP+BPF_JGT+BPF_K, (value), 1, 0), \
+	jt
+
+#define JLT32(value, jt) \
+	BPF_JUMP(BPF_JMP+BPF_JGE+BPF_K, (value), 1, 0), \
+	jt
+
+/*
+ * All the JXX64 checks assume lo is saved in M[0] and hi is saved in both
+ * A and M[1]. This invariant is kept by restoring A if necessary.
+ */
 #define JEQ64(lo, hi, jt) \
+	/* if (hi != arg.hi) goto NOMATCH; */ \
 	BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, (hi), 0, 5), \
 	BPF_STMT(BPF_LD+BPF_MEM, 0), /* swap in lo */ \
+	/* if (lo != arg.lo) goto NOMATCH; */ \
 	BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, (lo), 0, 2), \
-	BPF_STMT(BPF_LD+BPF_MEM, 1), /* passed: swap hi back in */ \
+	BPF_STMT(BPF_LD+BPF_MEM, 1), \
 	jt, \
-	BPF_STMT(BPF_LD+BPF_MEM, 1) /* failed: swap hi back in */
+	BPF_STMT(BPF_LD+BPF_MEM, 1)
 
 #define JNE64(lo, hi, jt) \
-	BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, (hi), 5, 0), \
-	BPF_STMT(BPF_LD+BPF_MEM, 0), /* swap in lo */ \
+	/* if (hi != arg.hi) goto MATCH; */ \
+	BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, (hi), 0, 3), \
+	BPF_STMT(BPF_LD+BPF_MEM, 0), \
+	/* if (lo != arg.lo) goto MATCH; */ \
 	BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, (lo), 2, 0), \
-	BPF_STMT(BPF_LD+BPF_MEM, 1), /* passed: swap hi back in */ \
+	BPF_STMT(BPF_LD+BPF_MEM, 1), \
 	jt, \
-	BPF_STMT(BPF_LD+BPF_MEM, 1) /* failed: swap hi back in */
-
-#define JA32(value, jt) \
-	BPF_JUMP(BPF_JMP+BPF_JSET+BPF_K, (value), 0, 1), \
-	jt
+	BPF_STMT(BPF_LD+BPF_MEM, 1)
 
 #define JA64(lo, hi, jt) \
+	/* if (hi & arg.hi) goto MATCH; */ \
 	BPF_JUMP(BPF_JMP+BPF_JSET+BPF_K, (hi), 3, 0), \
-	BPF_STMT(BPF_LD+BPF_MEM, 0), /* swap in lo */ \
+	BPF_STMT(BPF_LD+BPF_MEM, 0), \
+	/* if (lo & arg.lo) goto MATCH; */ \
 	BPF_JUMP(BPF_JMP+BPF_JSET+BPF_K, (lo), 0, 2), \
-	BPF_STMT(BPF_LD+BPF_MEM, 1), /* passed: swap hi back in */ \
+	BPF_STMT(BPF_LD+BPF_MEM, 1), \
 	jt, \
-	BPF_STMT(BPF_LD+BPF_MEM, 1) /* failed: swap hi back in */
+	BPF_STMT(BPF_LD+BPF_MEM, 1)
 
-#define JGE32(value, jt) \
-	BPF_JUMP(BPF_JMP+BPF_JGE+BPF_K, (value), 0, 1), \
-	jt
-
-#define JLT32(value, jt) \
-	BPF_JUMP(BPF_JMP+BPF_JGE+BPF_K, (value), 1, 0), \
-	jt
-
-/* Shortcut checking if hi > arg.hi. */
 #define JGE64(lo, hi, jt) \
+	/* if (hi > arg.hi) goto MATCH; */ \
 	BPF_JUMP(BPF_JMP+BPF_JGT+BPF_K, (hi), 4, 0), \
+	/* if (hi != arg.hi) goto NOMATCH; */ \
 	BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, (hi), 0, 5), \
-	BPF_STMT(BPF_LD+BPF_MEM, 0), /* swap in lo */ \
+	BPF_STMT(BPF_LD+BPF_MEM, 0), \
+	/* if (lo >= arg.lo) goto MATCH; */ \
 	BPF_JUMP(BPF_JMP+BPF_JGE+BPF_K, (lo), 0, 2), \
-	BPF_STMT(BPF_LD+BPF_MEM, 1), /* passed: swap hi back in */ \
-	jt, \
-	BPF_STMT(BPF_LD+BPF_MEM, 1) /* failed: swap hi back in */
-
-#define JLT64(lo, hi, jt) \
-	BPF_JUMP(BPF_JMP+BPF_JGE+BPF_K, (hi), 0, 4), \
-	BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, (hi), 0, 5), \
-	BPF_STMT(BPF_LD+BPF_MEM, 0), /* swap in lo */ \
-	BPF_JUMP(BPF_JMP+BPF_JGT+BPF_K, (lo), 2, 0), \
-	BPF_STMT(BPF_LD+BPF_MEM, 1), /* passed: swap hi back in */ \
+	BPF_STMT(BPF_LD+BPF_MEM, 1), \
 	jt, \
-	BPF_STMT(BPF_LD+BPF_MEM, 1) /* failed: swap hi back in */
+	BPF_STMT(BPF_LD+BPF_MEM, 1)
 
-#define JGT32(value, jt) \
-	BPF_JUMP(BPF_JMP+BPF_JGT+BPF_K, (value), 0, 1), \
-	jt
-
-#define JLE32(value, jt) \
-	BPF_JUMP(BPF_JMP+BPF_JGT+BPF_K, (value), 1, 0), \
-	jt
-
-/* Check hi > args.hi first, then do the GE checking */
 #define JGT64(lo, hi, jt) \
+	/* if (hi > arg.hi) goto MATCH; */ \
 	BPF_JUMP(BPF_JMP+BPF_JGT+BPF_K, (hi), 4, 0), \
+	/* if (hi != arg.hi) goto NOMATCH; */ \
 	BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, (hi), 0, 5), \
-	BPF_STMT(BPF_LD+BPF_MEM, 0), /* swap in lo */ \
+	BPF_STMT(BPF_LD+BPF_MEM, 0), \
+	/* if (lo > arg.lo) goto MATCH; */ \
 	BPF_JUMP(BPF_JMP+BPF_JGT+BPF_K, (lo), 0, 2), \
-	BPF_STMT(BPF_LD+BPF_MEM, 1), /* passed: swap hi back in */ \
+	BPF_STMT(BPF_LD+BPF_MEM, 1), \
 	jt, \
-	BPF_STMT(BPF_LD+BPF_MEM, 1) /* failed: swap hi back in */
+	BPF_STMT(BPF_LD+BPF_MEM, 1)
 
 #define JLE64(lo, hi, jt) \
-	BPF_JUMP(BPF_JMP+BPF_JGT+BPF_K, (hi), 6, 0), \
-	BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, (hi), 0, 3), \
-	BPF_STMT(BPF_LD+BPF_MEM, 0), /* swap in lo */ \
+	/* if (hi < arg.hi) goto MATCH; */ \
+	BPF_JUMP(BPF_JMP+BPF_JGE+BPF_K, (hi), 0, 4), \
+	/* if (hi != arg.hi) goto NOMATCH; */ \
+	BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, (hi), 0, 5), \
+	BPF_STMT(BPF_LD+BPF_MEM, 0), \
+	/* if (lo <= arg.lo) goto MATCH; */ \
 	BPF_JUMP(BPF_JMP+BPF_JGT+BPF_K, (lo), 2, 0), \
-	BPF_STMT(BPF_LD+BPF_MEM, 1), /* passed: swap hi back in */ \
+	BPF_STMT(BPF_LD+BPF_MEM, 1), \
+	jt, \
+	BPF_STMT(BPF_LD+BPF_MEM, 1)
+
+#define JLT64(lo, hi, jt) \
+	/* if (hi < arg.hi) goto MATCH; */ \
+	BPF_JUMP(BPF_JMP+BPF_JGE+BPF_K, (hi), 0, 4), \
+	/* if (hi != arg.hi) goto NOMATCH; */ \
+	BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, (hi), 0, 5), \
+	BPF_STMT(BPF_LD+BPF_MEM, 0), \
+	/* if (lo < arg.lo) goto MATCH; */ \
+	BPF_JUMP(BPF_JMP+BPF_JGE+BPF_K, (lo), 2, 0), \
+	BPF_STMT(BPF_LD+BPF_MEM, 1), \
 	jt, \
-	BPF_STMT(BPF_LD+BPF_MEM, 1) /* failed: swap hi back in */
+	BPF_STMT(BPF_LD+BPF_MEM, 1)
 
 #define LOAD_SYSCALL_NR \
 	BPF_STMT(BPF_LD+BPF_W+BPF_ABS, \