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Re: [PATCH v2 11/14] target/arm: Implement gdbstub pauth extension

From: Luis Machado
Subject: Re: [PATCH v2 11/14] target/arm: Implement gdbstub pauth extension
Date: Tue, 21 Feb 2023 09:14:50 +0000
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.7.1 
Hi,

On 2/21/23 02:19, Richard Henderson wrote:

The extension is primarily defined by the Linux kernel NT_ARM_PAC_MASK
ptrace register set.

The original gdb feature consists of two masks, data and code, which are
used to mask out the authentication code within a pointer.  Following
discussion with Luis Machado, add two more masks in order to support
pointers within the high half of the address space (i.e. TTBR1 vs TTBR0).

Cc: Luis Machado <luis.machado@arm.com>
Cc: Thiago Jung Bauermann <thiago.bauermann@linaro.org>
Resolves: https://gitlab.com/qemu-project/qemu/-/issues/1105
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
---
  configs/targets/aarch64-linux-user.mak    |  2 +-
  configs/targets/aarch64-softmmu.mak       |  2 +-
  configs/targets/aarch64_be-linux-user.mak |  2 +-
  target/arm/internals.h                    |  2 ++
  target/arm/gdbstub.c                      |  5 ++++
  target/arm/gdbstub64.c                    | 34 +++++++++++++++++++++++
  gdb-xml/aarch64-pauth.xml                 | 15 ++++++++++
  7 files changed, 59 insertions(+), 3 deletions(-)
  create mode 100644 gdb-xml/aarch64-pauth.xml

diff --git a/configs/targets/aarch64-linux-user.mak 
b/configs/targets/aarch64-linux-user.mak
index db552f1839..ba8bc5fe3f 100644
--- a/configs/targets/aarch64-linux-user.mak
+++ b/configs/targets/aarch64-linux-user.mak
@@ -1,6 +1,6 @@
  TARGET_ARCH=aarch64
  TARGET_BASE_ARCH=arm
-TARGET_XML_FILES= gdb-xml/aarch64-core.xml gdb-xml/aarch64-fpu.xml
+TARGET_XML_FILES= gdb-xml/aarch64-core.xml gdb-xml/aarch64-fpu.xml 
gdb-xml/aarch64-pauth.xml
  TARGET_HAS_BFLT=y
  CONFIG_SEMIHOSTING=y
  CONFIG_ARM_COMPATIBLE_SEMIHOSTING=y
diff --git a/configs/targets/aarch64-softmmu.mak 
b/configs/targets/aarch64-softmmu.mak
index d489e6da83..b4338e9568 100644
--- a/configs/targets/aarch64-softmmu.mak
+++ b/configs/targets/aarch64-softmmu.mak
@@ -1,5 +1,5 @@
  TARGET_ARCH=aarch64
  TARGET_BASE_ARCH=arm
  TARGET_SUPPORTS_MTTCG=y
-TARGET_XML_FILES= gdb-xml/aarch64-core.xml gdb-xml/aarch64-fpu.xml 
gdb-xml/arm-core.xml gdb-xml/arm-vfp.xml gdb-xml/arm-vfp3.xml 
gdb-xml/arm-vfp-sysregs.xml gdb-xml/arm-neon.xml gdb-xml/arm-m-profile.xml 
gdb-xml/arm-m-profile-mve.xml
+TARGET_XML_FILES= gdb-xml/aarch64-core.xml gdb-xml/aarch64-fpu.xml 
gdb-xml/arm-core.xml gdb-xml/arm-vfp.xml gdb-xml/arm-vfp3.xml 
gdb-xml/arm-vfp-sysregs.xml gdb-xml/arm-neon.xml gdb-xml/arm-m-profile.xml 
gdb-xml/arm-m-profile-mve.xml gdb-xml/aarch64-pauth.xml
  TARGET_NEED_FDT=y
diff --git a/configs/targets/aarch64_be-linux-user.mak 
b/configs/targets/aarch64_be-linux-user.mak
index dc78044fb1..acb5620cdb 100644
--- a/configs/targets/aarch64_be-linux-user.mak
+++ b/configs/targets/aarch64_be-linux-user.mak
@@ -1,7 +1,7 @@
  TARGET_ARCH=aarch64
  TARGET_BASE_ARCH=arm
  TARGET_BIG_ENDIAN=y
-TARGET_XML_FILES= gdb-xml/aarch64-core.xml gdb-xml/aarch64-fpu.xml
+TARGET_XML_FILES= gdb-xml/aarch64-core.xml gdb-xml/aarch64-fpu.xml 
gdb-xml/aarch64-pauth.xml
  TARGET_HAS_BFLT=y
  CONFIG_SEMIHOSTING=y
  CONFIG_ARM_COMPATIBLE_SEMIHOSTING=y
diff --git a/target/arm/internals.h b/target/arm/internals.h
index 370655061e..fb88b16579 100644
--- a/target/arm/internals.h
+++ b/target/arm/internals.h
@@ -1331,6 +1331,8 @@ int aarch64_gdb_get_sve_reg(CPUARMState *env, GByteArray 
*buf, int reg);
  int aarch64_gdb_set_sve_reg(CPUARMState *env, uint8_t *buf, int reg);
  int aarch64_gdb_get_fpu_reg(CPUARMState *env, GByteArray *buf, int reg);
  int aarch64_gdb_set_fpu_reg(CPUARMState *env, uint8_t *buf, int reg);
+int aarch64_gdb_get_pauth_reg(CPUARMState *env, GByteArray *buf, int reg);
+int aarch64_gdb_set_pauth_reg(CPUARMState *env, uint8_t *buf, int reg);
  void arm_cpu_sve_finalize(ARMCPU *cpu, Error **errp);
  void arm_cpu_sme_finalize(ARMCPU *cpu, Error **errp);
  void arm_cpu_pauth_finalize(ARMCPU *cpu, Error **errp);
diff --git a/target/arm/gdbstub.c b/target/arm/gdbstub.c
index bf8aff7824..062c8d447a 100644
--- a/target/arm/gdbstub.c
+++ b/target/arm/gdbstub.c
@@ -355,6 +355,11 @@ void arm_cpu_register_gdb_regs_for_features(ARMCPU *cpu)
                                       aarch64_gdb_set_fpu_reg,
                                       34, "aarch64-fpu.xml", 0);
          }
+        if (isar_feature_aa64_pauth(&cpu->isar)) {
+            gdb_register_coprocessor(cs, aarch64_gdb_get_pauth_reg,
+                                     aarch64_gdb_set_pauth_reg,
+                                     4, "aarch64-pauth.xml", 0);
+        }
  #endif
      } else {
          if (arm_feature(env, ARM_FEATURE_NEON)) {
diff --git a/target/arm/gdbstub64.c b/target/arm/gdbstub64.c
index 3d9e9e97c8..3bee892fb7 100644
--- a/target/arm/gdbstub64.c
+++ b/target/arm/gdbstub64.c
@@ -210,6 +210,40 @@ int aarch64_gdb_set_sve_reg(CPUARMState *env, uint8_t 
*buf, int reg)
      return 0;
  }

+int aarch64_gdb_get_pauth_reg(CPUARMState *env, GByteArray *buf, int reg)
+{
+    switch (reg) {
+    case 0: /* pauth_dmask */
+    case 1: /* pauth_cmask */
+    case 2: /* pauth_dmask_high */
+    case 3: /* pauth_cmask_high */
+        /*
+         * Note that older versions of this feature only contained
+         * pauth_{d,c}mask, for use with Linux user processes, and
+         * thus exclusively in the low half of the address space.
+         *
+         * To support system mode, and to debug kernels, two new regs
+         * were added to cover the high half of the address space.
+         * For the purpose of pauth_ptr_mask, we can use any well-formed
+         * address within the address space half -- here, 0 and -1.
+         */
+        {
+            bool is_data = !(reg & 1);
+            bool is_high = reg & 2;
+            uint64_t mask = pauth_ptr_mask(env, -is_high, is_data);
+            return gdb_get_reg64(buf, mask);
+        }
+    default:
+        return 0;
+    }
+}
+
+int aarch64_gdb_set_pauth_reg(CPUARMState *env, uint8_t *buf, int reg)
+{
+    /* All pseudo registers are read-only. */
+    return 0;
+}
+
  static void output_vector_union_type(GString *s, int reg_width,
                                       const char *name)
  {
diff --git a/gdb-xml/aarch64-pauth.xml b/gdb-xml/aarch64-pauth.xml
new file mode 100644
index 0000000000..24af5f903c
--- /dev/null
+++ b/gdb-xml/aarch64-pauth.xml
@@ -0,0 +1,15 @@
+<?xml version="1.0"?>
+<!-- Copyright (C) 2018-2022 Free Software Foundation, Inc.
+
+     Copying and distribution of this file, with or without modification,
+     are permitted in any medium without royalty provided the copyright
+     notice and this notice are preserved.  -->
+
+<!DOCTYPE feature SYSTEM "gdb-target.dtd">
+<feature name="org.gnu.gdb.aarch64.pauth">
+  <reg name="pauth_dmask" bitsize="64"/>
+  <reg name="pauth_cmask" bitsize="64"/>
+  <reg name="pauth_dmask_high" bitsize="64"/>
+  <reg name="pauth_cmask_high" bitsize="64"/>
+</feature>
+


FTR, I've pushed the gdb-side changes: 
https://sourceware.org/git/?p=binutils-gdb.git;a=commit;h=6d0020873deb2f2c4e0965dc2ebf227bc1db3140
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