target/arm: Fix output of PAuth Auth

The ARM pseudocode installs the error_code into the original
pointer, not the encrypted pointer.  The difference applies
within the 7 bits of pac data; the result should be the sign
extension of bit 55.

Add a testcase to that effect.

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

target/arm/pauth_helper.c

@@ -344,9 +344,9 @@ static uint64_t pauth_auth(CPUARMState *env, uint64_t ptr, uint64_t modifier,
     if (unlikely(extract64(test, bot_bit, top_bit - bot_bit))) {
         int error_code = (keynumber << 1) | (keynumber ^ 1);
         if (param.tbi) {
-            return deposit64(ptr, 53, 2, error_code);
+            return deposit64(orig_ptr, 53, 2, error_code);
         } else {
-            return deposit64(ptr, 61, 2, error_code);
+            return deposit64(orig_ptr, 61, 2, error_code);
         }
     }
     return orig_ptr;

tests/tcg/aarch64/Makefile.target

@@ -15,7 +15,7 @@ run-fcvt: fcvt
 	$(call run-test,$<,$(QEMU) $<, "$< on $(TARGET_NAME)")
 	$(call diff-out,$<,$(AARCH64_SRC)/fcvt.ref)
 
-AARCH64_TESTS += pauth-1
+AARCH64_TESTS += pauth-1 pauth-2
 run-pauth-%: QEMU += -cpu max
 
 TESTS:=$(AARCH64_TESTS)

tests/tcg/aarch64/pauth-2.c

@@ -0,0 +1,61 @@
+#include <stdint.h>
+#include <assert.h>
+
+asm(".arch armv8.4-a");
+
+void do_test(uint64_t value)
+{
+    uint64_t salt1, salt2;
+    uint64_t encode, decode;
+
+    /*
+     * With TBI enabled and a 48-bit VA, there are 7 bits of auth,
+     * and so a 1/128 chance of encode = pac(value,key,salt) producing
+     * an auth for which leaves value unchanged.
+     * Iterate until we find a salt for which encode != value.
+     */
+    for (salt1 = 1; ; salt1++) {
+        asm volatile("pacda %0, %2" : "=r"(encode) : "0"(value), "r"(salt1));
+        if (encode != value) {
+            break;
+        }
+    }
+
+    /* A valid salt must produce a valid authorization.  */
+    asm volatile("autda %0, %2" : "=r"(decode) : "0"(encode), "r"(salt1));
+    assert(decode == value);
+
+    /*
+     * An invalid salt usually fails authorization, but again there
+     * is a chance of choosing another salt that works.
+     * Iterate until we find another salt which does fail.
+     */
+    for (salt2 = salt1 + 1; ; salt2++) {
+        asm volatile("autda %0, %2" : "=r"(decode) : "0"(encode), "r"(salt2));
+        if (decode != value) {
+            break;
+        }
+    }
+
+    /* The VA bits, bit 55, and the TBI bits, should be unchanged.  */
+    assert(((decode ^ value) & 0xff80ffffffffffffull) == 0);
+
+    /*
+     * Bits [54:53] are an error indicator based on the key used;
+     * the DA key above is keynumber 0, so error == 0b01.  Otherwise
+     * bit 55 of the original is sign-extended into the rest of the auth.
+     */
+    if ((value >> 55) & 1) {
+        assert(((decode >> 48) & 0xff) == 0b10111111);
+    } else {
+        assert(((decode >> 48) & 0xff) == 0b00100000);
+    }
+}
+
+int main()
+{
+    do_test(0);
+    do_test(-1);
+    do_test(0xda004acedeadbeefull);
+    return 0;
+}