[BFD, LD, AArch64, 3/3] Add --pac-plt to enable PLTs protected with PAC.

This is part of the patch series to add support for BTI and
PAC in AArch64 linker.

1) This patch adds new definitions of PAC enabled PLTs
and both BTI and PAC enabled PLTs.
2) It also defines the new dynamic tag DT_AARCH64_PAC_PLT
for the PAC enabled PLTs.
3) This patch adds a new ld command line option: --pac-plt.
In the presence of this option, the linker uses the PAC
enabled PLTs and marks with DT_AARCH64_PAC_PLT.
4) In case both BTI and PAC are enabled the linker should
pick PLTs enabled with both and also use dynamic tags for both.
All these are made according to the new AArch64 ELF ABI
https://developer.arm.com/docs/ihi0056/latest/elf-for-the-arm-64-bit-architecture-aarch64-abi-2018q4

*** bfd/ChangeLog ***

2019-03-13  Sudakshina Das  <sudi.das@arm.com>

	* elfnn-aarch64.c (PLT_PAC_ENTRY_SIZE, PLT_PAC_SMALL_ENTRY_SIZE): New.
	(PLT_BTI_PAC_ENTRY_SIZE, PLT_BTI_PAC_SMALL_ENTRY_SIZE): New.
	(setup_plt_values): Account for PAC or PAC and BTI enabled PLTs.
	(elfNN_aarch64_size_dynamic_sections): Add checks for PLT_BTI_PAC
	and PLT_PAC_PLT.
	(elfNN_aarch64_finish_dynamic_sections): Account for PLT_BTI_PAC.
	(get_plt_type): Add case for DT_AARCH64_PAC_PLT.
	(elfNN_aarch64_plt_sym_val): Add cases for PLT_BTI_PAC and PLT_PAC.

*** binutils/ChangeLog ***

2019-03-13  Sudakshina Das  <sudi.das@arm.com>

	* readelf.c (get_aarch64_dynamic_type): Add case for
	DT_AARCH64_PAC_PLT.
	(dynamic_section_aarch64_val): Likewise.

*** include/ChangeLog ***

2019-03-13  Sudakshina Das  <sudi.das@arm.com>

	* elf/aarch64.h (DT_AARCH64_PAC_PLT): New.

*** ld/ChangeLog ***

2019-03-13  Sudakshina Das  <sudi.das@arm.com>

	* NEWS: Document --pac-plt.
	* emultempl/aarch64elf.em (OPTION_PAC_PLT): New.
	(PARSE_AND_LIST_LONGOPTS, PARSE_AND_LIST_OPTIONS): Add pac-plt.
	(PARSE_AND_LIST_ARGS_CASES): Handle OPTION_PAC_PLT.
	* testsuite/ld-aarch64/aarch64-elf.exp: Add the following tests.
	* testsuite/ld-aarch64/bti-pac-plt-1.d: New test.
	* testsuite/ld-aarch64/bti-pac-plt-2.d: New test.
	* testsuite/ld-aarch64/pac-plt-1.d: New test.
	* testsuite/ld-aarch64/pac-plt-2.d: New test.
	* testsuite/ld-aarch64/bti-plt-1.s: Add .ifndef directive.

2 files changed, 145 insertions, 6 deletions

diff --git a/bfd/ChangeLog b/bfd/ChangeLog
index 6e7748e..540f737 100644
--- a/bfd/ChangeLog
+++ b/bfd/ChangeLog
@@ -1,4 +1,15 @@
 2019-03-13  Sudakshina Das  <sudi.das@arm.com>
+
+	* elfnn-aarch64.c (PLT_PAC_ENTRY_SIZE, PLT_PAC_SMALL_ENTRY_SIZE): New.
+	(PLT_BTI_PAC_ENTRY_SIZE, PLT_BTI_PAC_SMALL_ENTRY_SIZE): New.
+	(setup_plt_values): Account for PAC or PAC and BTI enabled PLTs.
+	(elfNN_aarch64_size_dynamic_sections): Add checks for PLT_BTI_PAC
+	and PLT_PAC_PLT.
+	(elfNN_aarch64_finish_dynamic_sections): Account for PLT_BTI_PAC.
+	(get_plt_type): Add case for DT_AARCH64_PAC_PLT.
+	(elfNN_aarch64_plt_sym_val): Add cases for PLT_BTI_PAC and PLT_PAC.
+
+2019-03-13  Sudakshina Das  <sudi.das@arm.com>
 	    Szabolcs Nagy  <szabolcs.nagy@arm.com>
 
 	* bfd-in.h (aarch64_plt_type, aarch64_enable_bti_type): New.
diff --git a/bfd/elfnn-aarch64.c b/bfd/elfnn-aarch64.c
index 69b8f83..50541f0 100644
--- a/bfd/elfnn-aarch64.c
+++ b/bfd/elfnn-aarch64.c
@@ -271,6 +271,12 @@
 #define PLT_BTI_ENTRY_SIZE		(36)
 #define PLT_BTI_SMALL_ENTRY_SIZE	(20)
 #define PLT_BTI_TLSDESC_ENTRY_SIZE	(36)
+/* PLT sizes with PAC insn.  */
+#define PLT_PAC_ENTRY_SIZE		(36)
+#define PLT_PAC_SMALL_ENTRY_SIZE	(20)
+/* PLT sizes with BTI and PAC insn.  */
+#define PLT_BTI_PAC_ENTRY_SIZE		(40)
+#define PLT_BTI_PAC_SMALL_ENTRY_SIZE	(24)
 
 /* Encoding of the nop instruction.  */
 #define INSN_NOP 0xd503201f
@@ -319,6 +325,44 @@ static const bfd_byte elfNN_aarch64_small_plt0_bti_entry[PLT_BTI_ENTRY_SIZE] =
   0x1f, 0x20, 0x03, 0xd5,	/* nop */
 };
 
+static const bfd_byte elfNN_aarch64_small_plt0_pac_entry[PLT_PAC_ENTRY_SIZE] =
+{
+  0xf0, 0x7b, 0xbf, 0xa9,	/* stp x16, x30, [sp, #-16]!  */
+  0x10, 0x00, 0x00, 0x90,	/* adrp x16, (GOT+16)  */
+#if ARCH_SIZE == 64
+  0x11, 0x0A, 0x40, 0xf9,	/* ldr x17, [x16, #PLT_GOT+0x10]  */
+  0x10, 0x42, 0x00, 0x91,	/* add x16, x16,#PLT_GOT+0x10   */
+#else
+  0x11, 0x0A, 0x40, 0xb9,	/* ldr w17, [x16, #PLT_GOT+0x8]  */
+  0x10, 0x22, 0x00, 0x11,	/* add w16, w16,#PLT_GOT+0x8   */
+#endif
+  0x9f, 0x21, 0x03, 0xd5,	/* autia1716 */
+  0x20, 0x02, 0x1f, 0xd6,	/* br x17  */
+  0x1f, 0x20, 0x03, 0xd5,	/* nop */
+  0x1f, 0x20, 0x03, 0xd5,	/* nop */
+  0x1f, 0x20, 0x03, 0xd5,	/* nop */
+};
+
+static const bfd_byte
+elfNN_aarch64_small_plt0_bti_pac_entry[PLT_BTI_PAC_ENTRY_SIZE] =
+{
+  0x5f, 0x24, 0x03, 0xd5,	/* bti c.  */
+  0xf0, 0x7b, 0xbf, 0xa9,	/* stp x16, x30, [sp, #-16]!  */
+  0x10, 0x00, 0x00, 0x90,	/* adrp x16, (GOT+16)  */
+#if ARCH_SIZE == 64
+  0x11, 0x0A, 0x40, 0xf9,	/* ldr x17, [x16, #PLT_GOT+0x10]  */
+  0x10, 0x42, 0x00, 0x91,	/* add x16, x16,#PLT_GOT+0x10   */
+#else
+  0x11, 0x0A, 0x40, 0xb9,	/* ldr w17, [x16, #PLT_GOT+0x8]  */
+  0x10, 0x22, 0x00, 0x11,	/* add w16, w16,#PLT_GOT+0x8   */
+#endif
+  0x9f, 0x21, 0x03, 0xd5,	/* autia1716 */
+  0x20, 0x02, 0x1f, 0xd6,	/* br x17  */
+  0x1f, 0x20, 0x03, 0xd5,	/* nop */
+  0x1f, 0x20, 0x03, 0xd5,	/* nop */
+  0x1f, 0x20, 0x03, 0xd5,	/* nop */
+};
+
 /* Per function entry in a procedure linkage table looks like this
    if the distance between the PLTGOT and the PLT is < 4GB use
    these PLT entries.  Use BTI versions of the PLTs when enabled.  */
@@ -351,6 +395,37 @@ elfNN_aarch64_small_plt_bti_entry[PLT_BTI_SMALL_ENTRY_SIZE] =
 };
 
 static const bfd_byte
+elfNN_aarch64_small_plt_pac_entry[PLT_PAC_SMALL_ENTRY_SIZE] =
+{
+  0x10, 0x00, 0x00, 0x90,	/* adrp x16, PLTGOT + n * 8  */
+#if ARCH_SIZE == 64
+  0x11, 0x02, 0x40, 0xf9,	/* ldr x17, [x16, PLTGOT + n * 8] */
+  0x10, 0x02, 0x00, 0x91,	/* add x16, x16, :lo12:PLTGOT + n * 8  */
+#else
+  0x11, 0x02, 0x40, 0xb9,	/* ldr w17, [x16, PLTGOT + n * 4] */
+  0x10, 0x02, 0x00, 0x11,	/* add w16, w16, :lo12:PLTGOT + n * 4  */
+#endif
+  0x9f, 0x21, 0x03, 0xd5,	/* autia1716 */
+  0x20, 0x02, 0x1f, 0xd6,	/* br x17.  */
+};
+
+static const bfd_byte
+elfNN_aarch64_small_plt_bti_pac_entry[PLT_BTI_PAC_SMALL_ENTRY_SIZE] =
+{
+  0x5f, 0x24, 0x03, 0xd5,	/* bti c.  */
+  0x10, 0x00, 0x00, 0x90,	/* adrp x16, PLTGOT + n * 8  */
+#if ARCH_SIZE == 64
+  0x11, 0x02, 0x40, 0xf9,	/* ldr x17, [x16, PLTGOT + n * 8] */
+  0x10, 0x02, 0x00, 0x91,	/* add x16, x16, :lo12:PLTGOT + n * 8  */
+#else
+  0x11, 0x02, 0x40, 0xb9,	/* ldr w17, [x16, PLTGOT + n * 4] */
+  0x10, 0x02, 0x00, 0x11,	/* add w16, w16, :lo12:PLTGOT + n * 4  */
+#endif
+  0x9f, 0x21, 0x03, 0xd5,	/* autia1716 */
+  0x20, 0x02, 0x1f, 0xd6,	/* br x17.  */
+};
+
+static const bfd_byte
 elfNN_aarch64_tlsdesc_small_plt_entry[PLT_TLSDESC_ENTRY_SIZE] =
 {
   0xe2, 0x0f, 0xbf, 0xa9,	/* stp x2, x3, [sp, #-16]! */
@@ -4681,7 +4756,25 @@ setup_plt_values (struct bfd_link_info *link_info,
   struct elf_aarch64_link_hash_table *globals;
   globals = elf_aarch64_hash_table (link_info);
 
-  if (plt_type == PLT_BTI)
+  if (plt_type == PLT_BTI_PAC)
+    {
+      globals->plt_header_size = PLT_BTI_PAC_ENTRY_SIZE;
+      globals->plt0_entry = elfNN_aarch64_small_plt0_bti_pac_entry;
+      globals->tlsdesc_plt_entry_size = PLT_BTI_TLSDESC_ENTRY_SIZE;
+
+      /* Only in ET_EXEC we need PLTn with BTI.  */
+      if (bfd_link_pde (link_info))
+	{
+	  globals->plt_entry_size = PLT_BTI_PAC_SMALL_ENTRY_SIZE;
+	  globals->plt_entry = elfNN_aarch64_small_plt_bti_pac_entry;
+	}
+      else
+	{
+	  globals->plt_entry_size = PLT_PAC_SMALL_ENTRY_SIZE;
+	  globals->plt_entry = elfNN_aarch64_small_plt_pac_entry;
+	}
+    }
+  else if (plt_type == PLT_BTI)
     {
       globals->plt_header_size = PLT_BTI_ENTRY_SIZE;
       globals->plt0_entry = elfNN_aarch64_small_plt0_bti_entry;
@@ -4694,6 +4787,14 @@ setup_plt_values (struct bfd_link_info *link_info,
 	  globals->plt_entry = elfNN_aarch64_small_plt_bti_entry;
 	}
     }
+  else if (plt_type == PLT_PAC)
+    {
+      globals->plt_header_size = PLT_PAC_ENTRY_SIZE;
+      globals->plt0_entry = elfNN_aarch64_small_plt0_pac_entry;
+      globals->tlsdesc_plt_entry_size = PLT_TLSDESC_ENTRY_SIZE;
+      globals->plt_entry_size = PLT_PAC_SMALL_ENTRY_SIZE;
+      globals->plt_entry = elfNN_aarch64_small_plt_pac_entry;
+    }
 }
 
 /* Set option values needed during linking.  */
@@ -9077,8 +9178,17 @@ elfNN_aarch64_size_dynamic_sections (bfd *output_bfd ATTRIBUTE_UNUSED,
 		  || !add_dynamic_entry (DT_TLSDESC_GOT, 0)))
 	    return FALSE;
 
-	  if ((elf_aarch64_tdata (output_bfd)->plt_type == PLT_BTI)
-	      && !add_dynamic_entry (DT_AARCH64_BTI_PLT, 0))
+	  if ((elf_aarch64_tdata (output_bfd)->plt_type == PLT_BTI_PAC)
+	      && (!add_dynamic_entry (DT_AARCH64_BTI_PLT, 0)
+		  || !add_dynamic_entry (DT_AARCH64_PAC_PLT, 0)))
+	    return FALSE;
+
+	  else if ((elf_aarch64_tdata (output_bfd)->plt_type == PLT_BTI)
+		   && !add_dynamic_entry (DT_AARCH64_BTI_PLT, 0))
+	    return FALSE;
+
+	  else if ((elf_aarch64_tdata (output_bfd)->plt_type == PLT_PAC)
+		   && !add_dynamic_entry (DT_AARCH64_PAC_PLT, 0))
 	    return FALSE;
 	}
 
@@ -9604,7 +9714,7 @@ elfNN_aarch64_finish_dynamic_sections (bfd *output_bfd,
 	  htab->tlsdesc_plt_entry_size = PLT_TLSDESC_ENTRY_SIZE;
 
 	  aarch64_plt_type type = elf_aarch64_tdata (output_bfd)->plt_type;
-	  if (type == PLT_BTI)
+	  if (type == PLT_BTI || type == PLT_BTI_PAC)
 	    {
 	      entry = elfNN_aarch64_tlsdesc_small_plt_bti_entry;
 	      htab->tlsdesc_plt_entry_size = PLT_BTI_TLSDESC_ENTRY_SIZE;
@@ -9744,7 +9854,11 @@ get_plt_type (bfd *abfd)
       switch (tag)
 	{
 	case DT_AARCH64_BTI_PLT:
-	  ret = PLT_BTI;
+	  ret |= PLT_BTI;
+	  break;
+
+	case DT_AARCH64_PAC_PLT:
+	  ret |= PLT_PAC;
 	  break;
 
 	default: break;
@@ -9777,12 +9891,26 @@ elfNN_aarch64_plt_sym_val (bfd_vma i, const asection *plt,
   size_t plt0_size = PLT_ENTRY_SIZE;
   size_t pltn_size = PLT_SMALL_ENTRY_SIZE;
 
-  if (elf_aarch64_tdata (plt->owner)->plt_type == PLT_BTI)
+  if (elf_aarch64_tdata (plt->owner)->plt_type == PLT_BTI_PAC)
+    {
+      plt0_size = PLT_BTI_PAC_ENTRY_SIZE;
+      if (elf_elfheader (plt->owner)->e_type == ET_EXEC)
+	pltn_size = PLT_BTI_PAC_SMALL_ENTRY_SIZE;
+      else
+	pltn_size = PLT_PAC_SMALL_ENTRY_SIZE;
+    }
+  else if (elf_aarch64_tdata (plt->owner)->plt_type == PLT_BTI)
     {
       plt0_size = PLT_BTI_ENTRY_SIZE;
       if (elf_elfheader (plt->owner)->e_type == ET_EXEC)
 	pltn_size = PLT_BTI_SMALL_ENTRY_SIZE;
     }
+  else if (elf_aarch64_tdata (plt->owner)->plt_type == PLT_PAC)
+    {
+      plt0_size = PLT_PAC_ENTRY_SIZE;
+      pltn_size = PLT_PAC_SMALL_ENTRY_SIZE;
+    }
+
   return plt->vma + plt0_size + i * pltn_size;
 }