[PATCH] target/arm: Enable SCTLR_EL1.BT0 for aarch64-linux-user

[Richard Henderson <richard.henderson@linaro.org>]

This controls whether the PACI{A,B}SP instructions trap with BTYPE=3
(indirect branch from register other than x16/x17).  The linux kernel
sets this in bti_enable().

Resolves: https://gitlab.com/qemu-project/qemu/-/issues/998
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
---
 target/arm/cpu.c                  |  2 ++
 tests/tcg/aarch64/bti-3.c         | 42 +++++++++++++++++++++++++++++++
 tests/tcg/aarch64/Makefile.target |  8 +++---
 3 files changed, 48 insertions(+), 4 deletions(-)
 create mode 100644 tests/tcg/aarch64/bti-3.c

diff --git a/target/arm/cpu.c b/target/arm/cpu.c
index e3f8215203..c50a8dca0b 100644
--- a/target/arm/cpu.c
+++ b/target/arm/cpu.c
@@ -197,6 +197,8 @@ static void arm_cpu_reset(DeviceState *dev)
         /* Enable all PAC keys.  */
         env->cp15.sctlr_el[1] |= (SCTLR_EnIA | SCTLR_EnIB |
                                   SCTLR_EnDA | SCTLR_EnDB);
+        /* Trap on btype=3 for PACIxSP. */
+        env->cp15.sctlr_el[1] |= SCTLR_BT0;
         /* and to the FP/Neon instructions */
         env->cp15.cpacr_el1 = deposit64(env->cp15.cpacr_el1, 20, 2, 3);
         /* and to the SVE instructions */
diff --git a/tests/tcg/aarch64/bti-3.c b/tests/tcg/aarch64/bti-3.c
new file mode 100644
index 0000000000..a852856d9a
--- /dev/null
+++ b/tests/tcg/aarch64/bti-3.c
@@ -0,0 +1,42 @@
+/*
+ * BTI vs PACIASP
+ */
+
+#include "bti-crt.inc.c"
+
+static void skip2_sigill(int sig, siginfo_t *info, ucontext_t *uc)
+{
+    uc->uc_mcontext.pc += 8;
+    uc->uc_mcontext.pstate = 1;
+}
+
+#define BTYPE_1() \
+    asm("mov %0,#1; adr x16, 1f; br x16; 1: hint #25; mov %0,#0" \
+        : "=r"(skipped) : : "x16", "x30")
+
+#define BTYPE_2() \
+    asm("mov %0,#1; adr x16, 1f; blr x16; 1: hint #25; mov %0,#0" \
+        : "=r"(skipped) : : "x16", "x30")
+
+#define BTYPE_3() \
+    asm("mov %0,#1; adr x15, 1f; br x15; 1: hint #25; mov %0,#0" \
+        : "=r"(skipped) : : "x15", "x30")
+
+#define TEST(WHICH, EXPECT) \
+    do { WHICH(); fail += skipped ^ EXPECT; } while (0)
+
+int main()
+{
+    int fail = 0;
+    int skipped;
+
+    /* Signal-like with SA_SIGINFO.  */
+    signal_info(SIGILL, skip2_sigill);
+
+    /* With SCTLR_EL1.BT0 set, PACIASP is not compatible with type=3. */
+    TEST(BTYPE_1, 0);
+    TEST(BTYPE_2, 0);
+    TEST(BTYPE_3, 1);
+
+    return fail;
+}
diff --git a/tests/tcg/aarch64/Makefile.target b/tests/tcg/aarch64/Makefile.target
index 6ad0ad49f9..a738eb137c 100644
--- a/tests/tcg/aarch64/Makefile.target
+++ b/tests/tcg/aarch64/Makefile.target
@@ -26,11 +26,11 @@ run-plugin-pauth-%: QEMU_OPTS += -cpu max
 endif
 
 # BTI Tests
-# bti-1 tests the elf notes, so we require special compiler support.
+# bti-1 test the elf notes, so we require special compiler support.
 ifneq ($(CROSS_CC_HAS_ARMV8_BTI),)
-AARCH64_TESTS += bti-1
-bti-1: CFLAGS += -mbranch-protection=standard
-bti-1: LDFLAGS += -nostdlib
+AARCH64_TESTS += bti-1 bti-3
+bti-1 bti-3: CFLAGS += -mbranch-protection=standard
+bti-1 bti-3: LDFLAGS += -nostdlib
 endif
 # bti-2 tests PROT_BTI, so no special compiler support required.
 AARCH64_TESTS += bti-2
-- 
2.34.1