Re: [PATCH] libgcc: Fix uninitialized RA signing on AArch64 [PR107678]

[Wilco Dijkstra <Wilco.Dijkstra@arm.com>]

Hi,

> @Wilco, can you please send the rebased patch for patch review? We would
> need in out openSUSE package soon.

Here is an updated and rebased version:

Cheers,
Wilco

v4: rebase and add REG_UNSAVED_ARCHEXT.

A recent change only initializes the regs.how[] during Dwarf unwinding
which resulted in an uninitialized offset used in return address signing
and random failures during unwinding.  The fix is to encode the return
address signing state in REG_UNSAVED and a new state REG_UNSAVED_ARCHEXT.

Passes bootstrap & regress, OK for commit?

libgcc/
	PR target/107678
	* unwind-dw2.h (REG_UNSAVED_ARCHEXT): Add new enum.
	* unwind-dw2.c (uw_update_context_1): Add REG_UNSAVED_ARCHEXT case.
	* unwind-dw2-execute_cfa.h: Use REG_UNSAVED_ARCHEXT/REG_UNSAVED to 
	encode the return address signing state.
	* config/aarch64/aarch64-unwind.h (aarch64_demangle_return_addr)
	Check current return address signing state.
	(aarch64_frob_update_contex): Remove.

---
diff --git a/libgcc/config/aarch64/aarch64-unwind.h b/libgcc/config/aarch64/aarch64-unwind.h
index 874cf6c3e77fb72d999f51b636d74cb0b5728bbd..727c27ba5da983958b3134715d9d4d7c0af5c1e2 100644
--- a/libgcc/config/aarch64/aarch64-unwind.h
+++ b/libgcc/config/aarch64/aarch64-unwind.h
@@ -29,8 +29,6 @@ see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
 
 #define MD_DEMANGLE_RETURN_ADDR(context, fs, addr) \
   aarch64_demangle_return_addr (context, fs, addr)
-#define MD_FROB_UPDATE_CONTEXT(context, fs) \
-  aarch64_frob_update_context (context, fs)
 
 static inline int
 aarch64_cie_signed_with_b_key (struct _Unwind_Context *context)
@@ -55,42 +53,27 @@ aarch64_cie_signed_with_b_key (struct _Unwind_Context *context)
 
 static inline void *
 aarch64_demangle_return_addr (struct _Unwind_Context *context,
-			      _Unwind_FrameState *fs ATTRIBUTE_UNUSED,
+			      _Unwind_FrameState *fs,
 			      _Unwind_Word addr_word)
 {
   void *addr = (void *)addr_word;
-  if (context->flags & RA_SIGNED_BIT)
+  const int reg = DWARF_REGNUM_AARCH64_RA_STATE;
+
+  if (fs->regs.how[reg] == REG_UNSAVED)
+    return addr;
+
+  /* Return-address signing state is toggled by DW_CFA_GNU_window_save (where
+     REG_UNDEFINED means enabled), or set by a DW_CFA_expression.  */
+  if (fs->regs.how[reg] == REG_UNSAVED_ARCHEXT
+      || (_Unwind_GetGR (context, reg) & 0x1) != 0)
     {
       _Unwind_Word salt = (_Unwind_Word) context->cfa;
       if (aarch64_cie_signed_with_b_key (context) != 0)
 	return __builtin_aarch64_autib1716 (addr, salt);
       return __builtin_aarch64_autia1716 (addr, salt);
     }
-  else
-    return addr;
-}
-
-/* Do AArch64 private initialization on CONTEXT based on frame info FS.  Mark
-   CONTEXT as return address signed if bit 0 of DWARF_REGNUM_AARCH64_RA_STATE is
-   set.  */
-
-static inline void
-aarch64_frob_update_context (struct _Unwind_Context *context,
-			     _Unwind_FrameState *fs)
-{
-  const int reg = DWARF_REGNUM_AARCH64_RA_STATE;
-  int ra_signed;
-  if (fs->regs.how[reg] == REG_UNSAVED)
-    ra_signed = fs->regs.reg[reg].loc.offset & 0x1;
-  else
-    ra_signed = _Unwind_GetGR (context, reg) & 0x1;
-  if (ra_signed)
-    /* The flag is used for re-authenticating EH handler's address.  */
-    context->flags |= RA_SIGNED_BIT;
-  else
-    context->flags &= ~RA_SIGNED_BIT;
 
-  return;
+  return addr;
 }
 
 #endif /* defined AARCH64_UNWIND_H && defined __ILP32__ */
diff --git a/libgcc/unwind-dw2-execute_cfa.h b/libgcc/unwind-dw2-execute_cfa.h
index 264c11c03ec4a09cac2c19a241c5b110b1b6b602..aef377092ceede6bdda8532679f9b081c98fadce 100644
--- a/libgcc/unwind-dw2-execute_cfa.h
+++ b/libgcc/unwind-dw2-execute_cfa.h
@@ -278,10 +278,15 @@
 	case DW_CFA_GNU_window_save:
 #if defined (__aarch64__) && !defined (__ILP32__)
 	  /* This CFA is multiplexed with Sparc.  On AArch64 it's used to toggle
-	     return address signing status.  */
+	     return address signing status.  REG_UNSAVED/REG_UNSAVED_ARCHEXT
+	     mean RA signing is disabled/enabled.  */
 	  reg = DWARF_REGNUM_AARCH64_RA_STATE;
-	  gcc_assert (fs->regs.how[reg] == REG_UNSAVED);
-	  fs->regs.reg[reg].loc.offset ^= 1;
+	  gcc_assert (fs->regs.how[reg] == REG_UNSAVED
+		      || fs->regs.how[reg] == REG_UNSAVED_ARCHEXT);
+	  if (fs->regs.how[reg] == REG_UNSAVED)
+	    fs->regs.how[reg] = REG_UNSAVED_ARCHEXT;
+	  else
+	    fs->regs.how[reg] = REG_UNSAVED;
 #else
 	  /* ??? Hardcoded for SPARC register window configuration.  */
 	  if (__LIBGCC_DWARF_FRAME_REGISTERS__ >= 32)
diff --git a/libgcc/unwind-dw2.h b/libgcc/unwind-dw2.h
index e2f81983e1dcf3df6aebde2454630b7bee87d597..53e1b183c7d60112a14411d3356c49cb39cd0de7 100644
--- a/libgcc/unwind-dw2.h
+++ b/libgcc/unwind-dw2.h
@@ -29,6 +29,7 @@ enum {
   REG_SAVED_EXP,
   REG_SAVED_VAL_OFFSET,
   REG_SAVED_VAL_EXP,
+  REG_UNSAVED_ARCHEXT,		/* Target specific extension.  */
   REG_UNDEFINED
 };
 
diff --git a/libgcc/unwind-dw2.c b/libgcc/unwind-dw2.c
index 9c5bf7821916d8ac8e10e25a7123cd03f848019a..d0afce7a9ea9f5b12a5a01ef1e940e1452b48cab 100644
--- a/libgcc/unwind-dw2.c
+++ b/libgcc/unwind-dw2.c
@@ -137,9 +137,6 @@ struct _Unwind_Context
 #define SIGNAL_FRAME_BIT ((~(_Unwind_Word) 0 >> 1) + 1)
   /* Context which has version/args_size/by_value fields.  */
 #define EXTENDED_CONTEXT_BIT ((~(_Unwind_Word) 0 >> 2) + 1)
-  /* Bit reserved on AArch64, return address has been signed with A or B
-     key.  */
-#define RA_SIGNED_BIT ((~(_Unwind_Word) 0 >> 3) + 1)
   _Unwind_Word flags;
   /* 0 for now, can be increased when further fields are added to
      struct _Unwind_Context.  */
@@ -1200,6 +1197,7 @@ uw_update_context_1 (struct _Unwind_Context *context, _Unwind_FrameState *fs)
       {
       case REG_UNSAVED:
       case REG_UNDEFINED:
+      case REG_UNSAVED_ARCHEXT:
 	break;
 
       case REG_SAVED_OFFSET: