[PATCH 2/4] rs6000: Emit ROP-mitigation instructions in prologue and epilogue

[Bill Schmidt <wschmidt@linux.ibm.com>]

2021-05-13  Bill Schmidt  <wschmidt@linux.ibm.com>

gcc/
	* config/rs6000/rs6000-internal.h (rs6000_stack): Add
	rop_hash_save_offset and rop_hash_size.
	* config/rs6000/rs6000-logue.c (rs6000_stack_info): Compute
	rop_hash_size and rop_hash_save_offset.
	(debug_stack_info): Dump rop_hash_save_offset and rop_hash_size.
	(rs6000_emit_prologue): Emit hashst[p] in prologue.
	(rs6000_emit_epilogue): Emit hashchk[p] in epilogue.
	* config/rs6000/rs6000.md (unspec): Add UNSPEC_HASHST and
	UNSPEC_HASHCHK.
	(hashst): New define_insn.
	(hashchk): Likewise.
---
 gcc/config/rs6000/rs6000-internal.h |  2 +
 gcc/config/rs6000/rs6000-logue.c    | 74 ++++++++++++++++++++++++++---
 gcc/config/rs6000/rs6000.md         | 47 ++++++++++++++++++
 3 files changed, 116 insertions(+), 7 deletions(-)

diff --git a/gcc/config/rs6000/rs6000-internal.h b/gcc/config/rs6000/rs6000-internal.h
index 428a7861a98..88cf9bd5692 100644
--- a/gcc/config/rs6000/rs6000-internal.h
+++ b/gcc/config/rs6000/rs6000-internal.h
@@ -39,6 +39,7 @@ typedef struct rs6000_stack {
   int gp_save_offset;		/* offset to save GP regs from initial SP */
   int fp_save_offset;		/* offset to save FP regs from initial SP */
   int altivec_save_offset;	/* offset to save AltiVec regs from initial SP */
+  int rop_hash_save_offset;	/* offset to save ROP hash from initial SP */
   int lr_save_offset;		/* offset to save LR from initial SP */
   int cr_save_offset;		/* offset to save CR from initial SP */
   int vrsave_save_offset;	/* offset to save VRSAVE from initial SP */
@@ -53,6 +54,7 @@ typedef struct rs6000_stack {
   int gp_size;			/* size of saved GP registers */
   int fp_size;			/* size of saved FP registers */
   int altivec_size;		/* size of saved AltiVec registers */
+  int rop_hash_size;		/* size of ROP hash slot */
   int cr_size;			/* size to hold CR if not in fixed area */
   int vrsave_size;		/* size to hold VRSAVE */
   int altivec_padding_size;	/* size of altivec alignment padding */
diff --git a/gcc/config/rs6000/rs6000-logue.c b/gcc/config/rs6000/rs6000-logue.c
index b0ac183ceff..13c00e740d6 100644
--- a/gcc/config/rs6000/rs6000-logue.c
+++ b/gcc/config/rs6000/rs6000-logue.c
@@ -595,19 +595,21 @@ rs6000_savres_strategy (rs6000_stack_t *info,
 		+---------------------------------------+
 		| Parameter save area (+padding*) (P)	|  32
 		+---------------------------------------+
-		| Alloca space (A)			|  32+P
+		| Optional ROP hash slot (R)		|  32+P
 		+---------------------------------------+
-		| Local variable space (L)		|  32+P+A
+		| Alloca space (A)			|  32+P+R
 		+---------------------------------------+
-		| Save area for AltiVec registers (W)	|  32+P+A+L
+		| Local variable space (L)		|  32+P+R+A
 		+---------------------------------------+
-		| AltiVec alignment padding (Y)		|  32+P+A+L+W
+		| Save area for AltiVec registers (W)	|  32+P+R+A+L
 		+---------------------------------------+
-		| Save area for GP registers (G)	|  32+P+A+L+W+Y
+		| AltiVec alignment padding (Y)		|  32+P+R+A+L+W
 		+---------------------------------------+
-		| Save area for FP registers (F)	|  32+P+A+L+W+Y+G
+		| Save area for GP registers (G)	|  32+P+R+A+L+W+Y
 		+---------------------------------------+
-	old SP->| back chain to caller's caller		|  32+P+A+L+W+Y+G+F
+		| Save area for FP registers (F)	|  32+P+R+A+L+W+Y+G
+		+---------------------------------------+
+	old SP->| back chain to caller's caller		|  32+P+R+A+L+W+Y+G+F
 		+---------------------------------------+
 
      * If the alloca area is present, the parameter save area is
@@ -716,6 +718,19 @@ rs6000_stack_info (void)
 
   /* Does this function call anything (apart from sibling calls)?  */
   info->calls_p = (!crtl->is_leaf || cfun->machine->ra_needs_full_frame);
+  info->rop_hash_size = 0;
+
+  if (TARGET_POWER10
+      && info->calls_p
+      && DEFAULT_ABI == ABI_ELFv2
+      && rs6000_rop_protect)
+    info->rop_hash_size = 8;
+  else if (rs6000_rop_protect && DEFAULT_ABI != ABI_ELFv2)
+    {
+      /* We can't check this in rs6000_option_override_internal since
+	 DEFAULT_ABI isn't established yet.  */
+      error ("%qs requires the ELFv2 ABI", "-mrop-protect");
+    }
 
   /* Determine if we need to save the condition code registers.  */
   if (save_reg_p (CR2_REGNO)
@@ -808,6 +823,11 @@ rs6000_stack_info (void)
 
 	  /* Adjust for AltiVec case.  */
 	  info->ehrd_offset = info->altivec_save_offset - ehrd_size;
+
+	  /* Adjust for ROP protection.  */
+	  info->rop_hash_save_offset
+	    = info->altivec_save_offset - info->rop_hash_size;
+	  info->ehrd_offset -= info->rop_hash_size;
 	}
       else
 	info->ehrd_offset = info->gp_save_offset - ehrd_size;
@@ -849,6 +869,7 @@ rs6000_stack_info (void)
 				  + info->gp_size
 				  + info->altivec_size
 				  + info->altivec_padding_size
+				  + info->rop_hash_size
 				  + ehrd_size
 				  + ehcr_size
 				  + info->cr_size
@@ -987,6 +1008,10 @@ debug_stack_info (rs6000_stack_t *info)
     fprintf (stderr, "\tvrsave_save_offset  = %5d\n",
 	     info->vrsave_save_offset);
 
+  if (info->rop_hash_size)
+    fprintf (stderr, "\trop_hash_save_offset = %5d\n",
+	     info->rop_hash_save_offset);
+
   if (info->lr_save_p)
     fprintf (stderr, "\tlr_save_offset      = %5d\n", info->lr_save_offset);
 
@@ -1026,6 +1051,9 @@ debug_stack_info (rs6000_stack_t *info)
     fprintf (stderr, "\taltivec_padding_size= %5d\n",
 	     info->altivec_padding_size);
 
+  if (info->rop_hash_size)
+    fprintf (stderr, "\trop_hash_size       = %5d\n", info->rop_hash_size);
+
   if (info->cr_size)
     fprintf (stderr, "\tcr_size             = %5d\n", info->cr_size);
 
@@ -3252,6 +3280,22 @@ rs6000_emit_prologue (void)
 	}
     }
 
+  /* The ROP hash store must occur before a stack frame is created,
+     since the hash operates on r1.  */
+  /* NOTE: The hashst isn't needed if we're going to do a sibcall,
+     but there's no way to know that here.  Harmless except for
+     performance, of course.  */
+  if (TARGET_POWER10 && rs6000_rop_protect && info->rop_hash_size != 0)
+    {
+      gcc_assert (DEFAULT_ABI == ABI_ELFv2);
+      rtx stack_ptr = gen_rtx_REG (Pmode, STACK_POINTER_REGNUM);
+      rtx addr = gen_rtx_PLUS (Pmode, stack_ptr,
+			       GEN_INT (info->rop_hash_save_offset));
+      rtx mem = gen_rtx_MEM (Pmode, addr);
+      rtx reg0 = gen_rtx_REG (Pmode, 0);
+      emit_insn (gen_hashst (mem, reg0));
+    }
+
   /* If we need to save CR, put it into r12 or r11.  Choose r12 except when
      r12 will be needed by out-of-line gpr save.  */
   cr_save_regno = ((DEFAULT_ABI == ABI_AIX || DEFAULT_ABI == ABI_ELFv2)
@@ -4980,6 +5024,22 @@ rs6000_emit_epilogue (enum epilogue_type epilogue_type)
       emit_insn (gen_add3_insn (sp_reg_rtx, sp_reg_rtx, sa));
     }
 
+  /* The ROP hash check must occur after the stack pointer is restored
+     (since the hash involves r1), and is not performed for a sibcall.  */
+  if (TARGET_POWER10
+      && rs6000_rop_protect
+      && info->rop_hash_size != 0
+      && epilogue_type != EPILOGUE_TYPE_SIBCALL)
+    {
+      gcc_assert (DEFAULT_ABI == ABI_ELFv2);
+      rtx stack_ptr = gen_rtx_REG (Pmode, STACK_POINTER_REGNUM);
+      rtx addr = gen_rtx_PLUS (Pmode, stack_ptr,
+			       GEN_INT (info->rop_hash_save_offset));
+      rtx mem = gen_rtx_MEM (Pmode, addr);
+      rtx reg0 = gen_rtx_REG (Pmode, 0);
+      emit_insn (gen_hashchk (reg0, mem));
+    }
+
   if (epilogue_type != EPILOGUE_TYPE_SIBCALL && restoring_FPRs_inline)
     {
       if (cfa_restores)
diff --git a/gcc/config/rs6000/rs6000.md b/gcc/config/rs6000/rs6000.md
index c8cdc42533c..ce58ecd6b73 100644
--- a/gcc/config/rs6000/rs6000.md
+++ b/gcc/config/rs6000/rs6000.md
@@ -154,6 +154,8 @@ (define_c_enum "unspec"
    UNSPEC_CNTTZDM
    UNSPEC_PDEPD
    UNSPEC_PEXTD
+   UNSPEC_HASHST
+   UNSPEC_HASHCHK
   ])
 
 ;;
@@ -14948,6 +14950,51 @@ (define_insn "*cmpeqb_internal"
   "TARGET_P9_MISC && TARGET_64BIT"
   "cmpeqb %0,%1,%2"
   [(set_attr "type" "logical")])
+
+
+;; ROP mitigation instructions.
+
+(define_insn "hashst"
+  [(set (match_operand:DI 0 "simple_offsettable_mem_operand" "=m")
+        (unspec:DI [(match_operand:DI 1 "int_reg_operand" "r")]
+	           UNSPEC_HASHST))]
+  "TARGET_POWER10 && rs6000_rop_protect"
+{
+  static char templ[14];
+  char p[2];
+
+  if (rs6000_privileged)
+    {
+      p[0] = 'p';
+      p[1] = 0;
+    }
+  else
+    p[0] = 0;
+  sprintf (templ, "hashst%s %%1,%%0", p);
+  return templ;
+}
+  [(set_attr "type" "store")])
+
+(define_insn "hashchk"
+  [(unspec_volatile [(match_operand:DI 0 "int_reg_operand" "r")
+		     (match_operand:DI 1 "simple_offsettable_mem_operand" "m")]
+		    UNSPEC_HASHCHK)]
+  "TARGET_POWER10 && rs6000_rop_protect"
+{
+  static char templ[15];
+  char p[2];
+
+  if (rs6000_privileged)
+    {
+      p[0] = 'p';
+      p[1] = 0;
+    }
+  else
+    p[0] = 0;
+  sprintf (templ, "hashchk%s %%0,%%1", p);
+  return templ;
+}
+  [(set_attr "type" "load")])
 \f
 
 (include "sync.md")
-- 
2.27.0