From 076073c96b3df6823f8e00fa525cd90f71eae347 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Andr=C3=A9=20Kempe?= <andre.kempe@arm.com>
Date: Fri, 15 Oct 2021 17:20:23 +0100
Subject: [PATCH] Enable PA and BTI for breakpad

Introduces Arm's Pointer Authentication and Branch Target Identification
to breakpad.

The changes are similar to changes for PA/BTI to Marl, see
https://github.com/google/marl/pull/204

Bug: 1145581
Change-Id: I6a770316ad333bfcfad2ce7f3c1ff78afb35c010
Reviewed-on: https://chromium-review.googlesource.com/c/breakpad/breakpad/+/3226471
Reviewed-by: Primiano Tucci <primiano@chromium.org>
---
 src/common/linux/breakpad_getcontext.S | 66 ++++++++++++++++++++++++++
 1 file changed, 66 insertions(+)

diff --git a/src/common/linux/breakpad_getcontext.S b/src/common/linux/breakpad_getcontext.S
index 528dba7a..2ebcf319 100644
--- a/src/common/linux/breakpad_getcontext.S
+++ b/src/common/linux/breakpad_getcontext.S
@@ -90,6 +90,47 @@ breakpad_getcontext:
 
 #elif defined(__aarch64__)
 
+#if defined(__ARM_FEATURE_PAC_DEFAULT) && __ARM_FEATURE_PAC_DEFAULT
+    // ENABLE_PAUTH must be defined to 1 since this value will be used in
+    // bitwise-shift later!
+    #define ENABLE_PAUTH 1
+
+    #if ((__ARM_FEATURE_PAC_DEFAULT&((1<<0)|(1<<1)))==0)
+        #error Pointer authentication defines no valid key!
+    #endif
+#else
+    #define ENABLE_PAUTH 0
+#endif
+
+#if defined(__ARM_FEATURE_BTI_DEFAULT) && (__ARM_FEATURE_BTI_DEFAULT==1)
+    // ENABLE_BTI must be defined to 1 since this value will be used in
+    // bitwise-shift later!
+    #define ENABLE_BTI 1
+#else
+    #define ENABLE_BTI 0
+#endif
+
+
+// Although Pointer Authentication and Branch Target Instructions are technically
+// seperate features they work together, i.e. the paciasp and pacibsp instructions
+// serve as BTI landing pads.
+// Therefore PA-instructions are enabled when PA _or_ BTI is enabled!
+#if ENABLE_PAUTH || ENABLE_BTI
+    // See section "Pointer Authentication" of
+    // https://developer.arm.com/documentation/101028/0012/5--Feature-test-macros
+    // for details how to interpret __ARM_FEATURE_PAC_DEFAULT
+    #if (__ARM_FEATURE_PAC_DEFAULT & (1<<0))
+        #define PAUTH_SIGN_SP paciasp
+        #define PAUTH_AUTH_SP autiasp
+    #else
+        #define PAUTH_SIGN_SP pacibsp
+        #define PAUTH_AUTH_SP autibsp
+    #endif
+#else
+    #define PAUTH_SIGN_SP
+    #define PAUTH_AUTH_SP
+#endif
+
 #define  _NSIG                       64
 #define  __NR_rt_sigprocmask         135
 
@@ -101,6 +142,8 @@ breakpad_getcontext:
   .cfi_startproc
 breakpad_getcontext:
 
+  PAUTH_SIGN_SP
+
   /* The saved context will return to the getcontext() call point
      with a return value of 0 */
   str     xzr,      [x0, MCONTEXT_GREGS_OFFSET +  0 * REGISTER_SIZE]
@@ -170,6 +213,9 @@ breakpad_getcontext:
 
   /* Return x0 for success */
   mov     x0, 0
+
+  PAUTH_AUTH_SP
+
   ret
 
   .cfi_endproc
@@ -484,3 +530,23 @@ breakpad_getcontext:
 #else
 #error "This file has not been ported for your CPU!"
 #endif
+
+#if defined(__aarch64__)
+// ENABLE_PAUTH and ENABLE_BTI would be enabled at the definition
+//  of AArch64 specific breakpad_getcontext function
+#if ENABLE_PAUTH || ENABLE_BTI
+// for further information on the .note.gnu.property section see
+// https://github.com/ARM-software/abi-aa/blob/main/aaelf64/aaelf64.rst#program-property
+.pushsection .note.gnu.property, "a";
+    .balign 8
+    .long 4
+    .long 0x10
+    .long 0x5
+    .asciz "GNU"
+    .long 0xc0000000 /* GNU_PROPERTY_AARCH64_FEATURE_1_AND */
+    .long 4
+    .long ((ENABLE_PAUTH)<<1) | ((ENABLE_BTI)<<0) /* PAuth and BTI */
+    .long 0
+.popsection
+#endif
+#endif