* [PATCH v2] gcc: mitigate the Straight-line Speculation attack
@ 2020-07-22 14:10 Ross Burton
0 siblings, 0 replies; only message in thread
From: Ross Burton @ 2020-07-22 14:10 UTC (permalink / raw)
To: openembedded-core
From: Ross Burton <ross.burton@arm.com>
Straight-line Speculation is a SPECTRE-like attack on Armv8-A, further
details can be found in the white paper here:
https://developer.arm.com/support/arm-security-updates/speculative-processor-vulnerability/downloads/straight-line-speculation
Backport the GCC patches to mitigate the attack.
CVE: CVE-2020-13844
Signed-off-by: Ross Burton <ross.burton@arm.com>
---
meta/recipes-devtools/gcc/gcc-10.1.inc | 3 +
...ight-Line-Speculation-SLS-mitigation.patch | 202 ++++++
...e-SLS-mitigation-for-RET-and-BR-inst.patch | 607 ++++++++++++++++
...h64-Mitigate-SLS-for-BLR-instruction.patch | 658 ++++++++++++++++++
4 files changed, 1470 insertions(+)
create mode 100644 meta/recipes-devtools/gcc/gcc-10.1/0001-aarch64-New-Straight-Line-Speculation-SLS-mitigation.patch
create mode 100644 meta/recipes-devtools/gcc/gcc-10.1/0002-aarch64-Introduce-SLS-mitigation-for-RET-and-BR-inst.patch
create mode 100644 meta/recipes-devtools/gcc/gcc-10.1/0003-aarch64-Mitigate-SLS-for-BLR-instruction.patch
diff --git a/meta/recipes-devtools/gcc/gcc-10.1.inc b/meta/recipes-devtools/gcc/gcc-10.1.inc
index a3de91a2c6..7c1201a2e3 100644
--- a/meta/recipes-devtools/gcc/gcc-10.1.inc
+++ b/meta/recipes-devtools/gcc/gcc-10.1.inc
@@ -66,6 +66,9 @@ SRC_URI = "\
file://0036-Enable-CET-in-cross-compiler-if-possible.patch \
file://0037-mingw32-Enable-operation_not_supported.patch \
file://0038-libatomic-Do-not-enforce-march-on-aarch64.patch \
+ file://0001-aarch64-New-Straight-Line-Speculation-SLS-mitigation.patch \
+ file://0002-aarch64-Introduce-SLS-mitigation-for-RET-and-BR-inst.patch \
+ file://0003-aarch64-Mitigate-SLS-for-BLR-instruction.patch \
"
SRC_URI[sha256sum] = "b6898a23844b656f1b68691c5c012036c2e694ac4b53a8918d4712ad876e7ea2"
diff --git a/meta/recipes-devtools/gcc/gcc-10.1/0001-aarch64-New-Straight-Line-Speculation-SLS-mitigation.patch b/meta/recipes-devtools/gcc/gcc-10.1/0001-aarch64-New-Straight-Line-Speculation-SLS-mitigation.patch
new file mode 100644
index 0000000000..73de4c7590
--- /dev/null
+++ b/meta/recipes-devtools/gcc/gcc-10.1/0001-aarch64-New-Straight-Line-Speculation-SLS-mitigation.patch
@@ -0,0 +1,202 @@
+CVE: CVE-2020-13844
+Upstream-Status: Backport
+Signed-off-by: Ross Burton <ross.burton@arm.com>
+
+From 1ff243934ac443b5f58cd02a5012ce58ecc31fb2 Mon Sep 17 00:00:00 2001
+From: Matthew Malcomson <matthew.malcomson@arm.com>
+Date: Thu, 9 Jul 2020 09:11:58 +0100
+Subject: [PATCH 1/3] aarch64: New Straight Line Speculation (SLS) mitigation
+ flags
+
+Here we introduce the flags that will be used for straight line speculation.
+
+The new flag introduced is `-mharden-sls=`.
+This flag can take arguments of `none`, `all`, or a comma seperated list of one
+or more of `retbr` or `blr`.
+`none` indicates no special mitigation of the straight line speculation
+vulnerability.
+`all` requests all mitigations currently implemented.
+`retbr` requests that the RET and BR instructions have a speculation barrier
+inserted after them.
+`blr` requests that BLR instructions are replaced by a BL to a function stub
+using a BR with a speculation barrier after it.
+
+Setting this on a per-function basis using attributes or the like is not
+enabled, but may be in the future.
+
+gcc/ChangeLog:
+
+2020-06-02 Matthew Malcomson <matthew.malcomson@arm.com>
+
+ * config/aarch64/aarch64-protos.h (aarch64_harden_sls_retbr_p):
+ New.
+ (aarch64_harden_sls_blr_p): New.
+ * config/aarch64/aarch64.c (enum aarch64_sls_hardening_type):
+ New.
+ (aarch64_harden_sls_retbr_p): New.
+ (aarch64_harden_sls_blr_p): New.
+ (aarch64_validate_sls_mitigation): New.
+ (aarch64_override_options): Parse options for SLS mitigation.
+ * config/aarch64/aarch64.opt (-mharden-sls): New option.
+ * doc/invoke.texi: Document new option.
+---
+ gcc/config/aarch64/aarch64-protos.h | 3 ++
+ gcc/config/aarch64/aarch64.c | 76 +++++++++++++++++++++++++++++++++++++
+ gcc/config/aarch64/aarch64.opt | 4 ++
+ gcc/doc/invoke.texi | 12 ++++++
+ 4 files changed, 95 insertions(+)
+
+diff --git a/gcc/config/aarch64/aarch64-protos.h b/gcc/config/aarch64/aarch64-protos.h
+index 723d9ba..eb5f4b4 100644
+--- a/gcc/config/aarch64/aarch64-protos.h
++++ b/gcc/config/aarch64/aarch64-protos.h
+@@ -781,4 +781,7 @@ extern const atomic_ool_names aarch64_ool_ldeor_names;
+
+ tree aarch64_resolve_overloaded_builtin_general (location_t, tree, void *);
+
++extern bool aarch64_harden_sls_retbr_p (void);
++extern bool aarch64_harden_sls_blr_p (void);
++
+ #endif /* GCC_AARCH64_PROTOS_H */
+diff --git a/gcc/config/aarch64/aarch64.c b/gcc/config/aarch64/aarch64.c
+index b86434a..437a9cf 100644
+--- a/gcc/config/aarch64/aarch64.c
++++ b/gcc/config/aarch64/aarch64.c
+@@ -14494,6 +14494,79 @@ aarch64_validate_mcpu (const char *str, const struct processor **res,
+ return false;
+ }
+
++/* Straight line speculation indicators. */
++enum aarch64_sls_hardening_type
++{
++ SLS_NONE = 0,
++ SLS_RETBR = 1,
++ SLS_BLR = 2,
++ SLS_ALL = 3,
++};
++static enum aarch64_sls_hardening_type aarch64_sls_hardening;
++
++/* Return whether we should mitigatate Straight Line Speculation for the RET
++ and BR instructions. */
++bool
++aarch64_harden_sls_retbr_p (void)
++{
++ return aarch64_sls_hardening & SLS_RETBR;
++}
++
++/* Return whether we should mitigatate Straight Line Speculation for the BLR
++ instruction. */
++bool
++aarch64_harden_sls_blr_p (void)
++{
++ return aarch64_sls_hardening & SLS_BLR;
++}
++
++/* As of yet we only allow setting these options globally, in the future we may
++ allow setting them per function. */
++static void
++aarch64_validate_sls_mitigation (const char *const_str)
++{
++ char *token_save = NULL;
++ char *str = NULL;
++
++ if (strcmp (const_str, "none") == 0)
++ {
++ aarch64_sls_hardening = SLS_NONE;
++ return;
++ }
++ if (strcmp (const_str, "all") == 0)
++ {
++ aarch64_sls_hardening = SLS_ALL;
++ return;
++ }
++
++ char *str_root = xstrdup (const_str);
++ str = strtok_r (str_root, ",", &token_save);
++ if (!str)
++ error ("invalid argument given to %<-mharden-sls=%>");
++
++ int temp = SLS_NONE;
++ while (str)
++ {
++ if (strcmp (str, "blr") == 0)
++ temp |= SLS_BLR;
++ else if (strcmp (str, "retbr") == 0)
++ temp |= SLS_RETBR;
++ else if (strcmp (str, "none") == 0 || strcmp (str, "all") == 0)
++ {
++ error ("%<%s%> must be by itself for %<-mharden-sls=%>", str);
++ break;
++ }
++ else
++ {
++ error ("invalid argument %<%s%> for %<-mharden-sls=%>", str);
++ break;
++ }
++ str = strtok_r (NULL, ",", &token_save);
++ }
++ aarch64_sls_hardening = (aarch64_sls_hardening_type) temp;
++ free (str_root);
++}
++
+ /* Parses CONST_STR for branch protection features specified in
+ aarch64_branch_protect_types, and set any global variables required. Returns
+ the parsing result and assigns LAST_STR to the last processed token from
+@@ -14738,6 +14811,9 @@ aarch64_override_options (void)
+ selected_arch = NULL;
+ selected_tune = NULL;
+
++ if (aarch64_harden_sls_string)
++ aarch64_validate_sls_mitigation (aarch64_harden_sls_string);
++
+ if (aarch64_branch_protection_string)
+ aarch64_validate_mbranch_protection (aarch64_branch_protection_string);
+
+diff --git a/gcc/config/aarch64/aarch64.opt b/gcc/config/aarch64/aarch64.opt
+index d99d14c..5170361 100644
+--- a/gcc/config/aarch64/aarch64.opt
++++ b/gcc/config/aarch64/aarch64.opt
+@@ -71,6 +71,10 @@ mgeneral-regs-only
+ Target Report RejectNegative Mask(GENERAL_REGS_ONLY) Save
+ Generate code which uses only the general registers.
+
++mharden-sls=
++Target RejectNegative Joined Var(aarch64_harden_sls_string)
++Generate code to mitigate against straight line speculation.
++
+ mfix-cortex-a53-835769
+ Target Report Var(aarch64_fix_a53_err835769) Init(2) Save
+ Workaround for ARM Cortex-A53 Erratum number 835769.
+diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
+index a2794a6..bd5b77a 100644
+--- a/gcc/doc/invoke.texi
++++ b/gcc/doc/invoke.texi
+@@ -696,6 +696,7 @@ Objective-C and Objective-C++ Dialects}.
+ -msign-return-address=@var{scope} @gol
+ -mbranch-protection=@var{none}|@var{standard}|@var{pac-ret}[+@var{leaf}
+ +@var{b-key}]|@var{bti} @gol
++-mharden-sls=@var{opts} @gol
+ -march=@var{name} -mcpu=@var{name} -mtune=@var{name} @gol
+ -moverride=@var{string} -mverbose-cost-dump @gol
+ -mstack-protector-guard=@var{guard} -mstack-protector-guard-reg=@var{sysreg} @gol
+@@ -17065,6 +17066,17 @@ functions. The optional argument @samp{b-key} can be used to sign the functions
+ with the B-key instead of the A-key.
+ @samp{bti} turns on branch target identification mechanism.
+
++@item -mharden-sls=@var{opts}
++@opindex mharden-sls
++Enable compiler hardening against straight line speculation (SLS).
++@var{opts} is a comma-separated list of the following options:
++@table @samp
++@item retbr
++@item blr
++@end table
++In addition, @samp{-mharden-sls=all} enables all SLS hardening while
++@samp{-mharden-sls=none} disables all SLS hardening.
++
+ @item -msve-vector-bits=@var{bits}
+ @opindex msve-vector-bits
+ Specify the number of bits in an SVE vector register. This option only has
+--
+2.7.4
+
diff --git a/meta/recipes-devtools/gcc/gcc-10.1/0002-aarch64-Introduce-SLS-mitigation-for-RET-and-BR-inst.patch b/meta/recipes-devtools/gcc/gcc-10.1/0002-aarch64-Introduce-SLS-mitigation-for-RET-and-BR-inst.patch
new file mode 100644
index 0000000000..823cc8b668
--- /dev/null
+++ b/meta/recipes-devtools/gcc/gcc-10.1/0002-aarch64-Introduce-SLS-mitigation-for-RET-and-BR-inst.patch
@@ -0,0 +1,607 @@
+Upstream-Status: Backport
+Signed-off-by: Ross Burton <ross.burton@arm.com>
+
+From b1204d16e1ec96a4aa89e44de8990e2499ffdb22 Mon Sep 17 00:00:00 2001
+From: Matthew Malcomson <matthew.malcomson@arm.com>
+Date: Thu, 9 Jul 2020 09:11:59 +0100
+Subject: [PATCH 2/3] aarch64: Introduce SLS mitigation for RET and BR
+ instructions
+
+Instructions following RET or BR are not necessarily executed. In order
+to avoid speculation past RET and BR we can simply append a speculation
+barrier.
+
+Since these speculation barriers will not be architecturally executed,
+they are not expected to add a high performance penalty.
+
+The speculation barrier is to be SB when targeting architectures which
+have this enabled, and DSB SY + ISB otherwise.
+
+We add tests for each of the cases where such an instruction was seen.
+
+This is implemented by modifying each machine description pattern that
+emits either a RET or a BR instruction. We choose not to use something
+like `TARGET_ASM_FUNCTION_EPILOGUE` since it does not affect the
+`indirect_jump`, `jump`, `sibcall_insn` and `sibcall_value_insn`
+patterns and we find it preferable to implement the functionality in the
+same way for every pattern.
+
+There is one particular case which is slightly tricky. The
+implementation of TARGET_ASM_TRAMPOLINE_TEMPLATE uses a BR which needs
+to be mitigated against. The trampoline template is used *once* per
+compilation unit, and the TRAMPOLINE_SIZE is exposed to the user via the
+builtin macro __LIBGCC_TRAMPOLINE_SIZE__.
+In the future we may implement function specific attributes to turn on
+and off hardening on a per-function basis.
+The fixed nature of the trampoline described above implies it will be
+safer to ensure this speculation barrier is always used.
+
+Testing:
+ Bootstrap and regtest done on aarch64-none-linux
+ Used a temporary hack(1) to use these options on every test in the
+ testsuite and a script to check that the output never emitted an
+ unmitigated RET or BR.
+
+1) Temporary hack was a change to the testsuite to always use
+`-save-temps` and run a script on the assembly output of those
+compilations which produced one to ensure every RET or BR is immediately
+followed by a speculation barrier.
+
+gcc/ChangeLog:
+
+ * config/aarch64/aarch64-protos.h (aarch64_sls_barrier): New.
+ * config/aarch64/aarch64.c (aarch64_output_casesi): Emit
+ speculation barrier after BR instruction if needs be.
+ (aarch64_trampoline_init): Handle ptr_mode value & adjust size
+ of code copied.
+ (aarch64_sls_barrier): New.
+ (aarch64_asm_trampoline_template): Add needed barriers.
+ * config/aarch64/aarch64.h (AARCH64_ISA_SB): New.
+ (TARGET_SB): New.
+ (TRAMPOLINE_SIZE): Account for barrier.
+ * config/aarch64/aarch64.md (indirect_jump, *casesi_dispatch,
+ simple_return, *do_return, *sibcall_insn, *sibcall_value_insn):
+ Emit barrier if needs be, also account for possible barrier using
+ "sls_length" attribute.
+ (sls_length): New attribute.
+ (length): Determine default using any non-default sls_length
+ value.
+
+gcc/testsuite/ChangeLog:
+
+ * gcc.target/aarch64/sls-mitigation/sls-miti-retbr.c: New test.
+ * gcc.target/aarch64/sls-mitigation/sls-miti-retbr-pacret.c:
+ New test.
+ * gcc.target/aarch64/sls-mitigation/sls-mitigation.exp: New file.
+ * lib/target-supports.exp (check_effective_target_aarch64_asm_sb_ok):
+ New proc.
+---
+ gcc/config/aarch64/aarch64-protos.h | 1 +
+ gcc/config/aarch64/aarch64.c | 41 ++++++-
+ gcc/config/aarch64/aarch64.h | 10 +-
+ gcc/config/aarch64/aarch64.md | 76 +++++++++----
+ .../aarch64/sls-mitigation/sls-miti-retbr-pacret.c | 21 ++++
+ .../aarch64/sls-mitigation/sls-miti-retbr.c | 119 +++++++++++++++++++++
+ .../aarch64/sls-mitigation/sls-mitigation.exp | 73 +++++++++++++
+ gcc/testsuite/lib/target-supports.exp | 2 +-
+ 8 files changed, 318 insertions(+), 25 deletions(-)
+ create mode 100644 gcc/testsuite/gcc.target/aarch64/sls-mitigation/sls-miti-retbr-pacret.c
+ create mode 100644 gcc/testsuite/gcc.target/aarch64/sls-mitigation/sls-miti-retbr.c
+ create mode 100644 gcc/testsuite/gcc.target/aarch64/sls-mitigation/sls-mitigation.exp
+
+diff --git a/gcc/config/aarch64/aarch64-protos.h b/gcc/config/aarch64/aarch64-protos.h
+index eb5f4b4..ee0ffde 100644
+--- a/gcc/config/aarch64/aarch64-protos.h
++++ b/gcc/config/aarch64/aarch64-protos.h
+@@ -781,6 +781,7 @@ extern const atomic_ool_names aarch64_ool_ldeor_names;
+
+ tree aarch64_resolve_overloaded_builtin_general (location_t, tree, void *);
+
++const char *aarch64_sls_barrier (int);
+ extern bool aarch64_harden_sls_retbr_p (void);
+ extern bool aarch64_harden_sls_blr_p (void);
+
+diff --git a/gcc/config/aarch64/aarch64.c b/gcc/config/aarch64/aarch64.c
+index 437a9cf..44e3d1f 100644
+--- a/gcc/config/aarch64/aarch64.c
++++ b/gcc/config/aarch64/aarch64.c
+@@ -10852,8 +10852,8 @@ aarch64_return_addr (int count, rtx frame ATTRIBUTE_UNUSED)
+ static void
+ aarch64_asm_trampoline_template (FILE *f)
+ {
+- int offset1 = 16;
+- int offset2 = 20;
++ int offset1 = 24;
++ int offset2 = 28;
+
+ if (aarch64_bti_enabled ())
+ {
+@@ -10876,6 +10876,17 @@ aarch64_asm_trampoline_template (FILE *f)
+ }
+ asm_fprintf (f, "\tbr\t%s\n", reg_names [IP1_REGNUM]);
+
++ /* We always emit a speculation barrier.
++ This is because the same trampoline template is used for every nested
++ function. Since nested functions are not particularly common or
++ performant we don't worry too much about the extra instructions to copy
++ around.
++ This is not yet a problem, since we have not yet implemented function
++ specific attributes to choose between hardening against straight line
++ speculation or not, but such function specific attributes are likely to
++ happen in the future. */
++ asm_fprintf (f, "\tdsb\tsy\n\tisb\n");
++
+ /* The trampoline needs an extra padding instruction. In case if BTI is
+ enabled the padding instruction is replaced by the BTI instruction at
+ the beginning. */
+@@ -10890,10 +10901,14 @@ static void
+ aarch64_trampoline_init (rtx m_tramp, tree fndecl, rtx chain_value)
+ {
+ rtx fnaddr, mem, a_tramp;
+- const int tramp_code_sz = 16;
++ const int tramp_code_sz = 24;
+
+ /* Don't need to copy the trailing D-words, we fill those in below. */
+- emit_block_move (m_tramp, assemble_trampoline_template (),
++ /* We create our own memory address in Pmode so that `emit_block_move` can
++ use parts of the backend which expect Pmode addresses. */
++ rtx temp = convert_memory_address (Pmode, XEXP (m_tramp, 0));
++ emit_block_move (gen_rtx_MEM (BLKmode, temp),
++ assemble_trampoline_template (),
+ GEN_INT (tramp_code_sz), BLOCK_OP_NORMAL);
+ mem = adjust_address (m_tramp, ptr_mode, tramp_code_sz);
+ fnaddr = XEXP (DECL_RTL (fndecl), 0);
+@@ -11084,6 +11099,8 @@ aarch64_output_casesi (rtx *operands)
+ output_asm_insn (buf, operands);
+ output_asm_insn (patterns[index][1], operands);
+ output_asm_insn ("br\t%3", operands);
++ output_asm_insn (aarch64_sls_barrier (aarch64_harden_sls_retbr_p ()),
++ operands);
+ assemble_label (asm_out_file, label);
+ return "";
+ }
+@@ -22924,6 +22941,22 @@ aarch64_file_end_indicate_exec_stack ()
+ #undef GNU_PROPERTY_AARCH64_FEATURE_1_BTI
+ #undef GNU_PROPERTY_AARCH64_FEATURE_1_AND
+
++/* Helper function for straight line speculation.
++ Return what barrier should be emitted for straight line speculation
++ mitigation.
++ When not mitigating against straight line speculation this function returns
++ an empty string.
++ When mitigating against straight line speculation, use:
++ * SB when the v8.5-A SB extension is enabled.
++ * DSB+ISB otherwise. */
++const char *
++aarch64_sls_barrier (int mitigation_required)
++{
++ return mitigation_required
++ ? (TARGET_SB ? "sb" : "dsb\tsy\n\tisb")
++ : "";
++}
++
+ /* Target-specific selftests. */
+
+ #if CHECKING_P
+diff --git a/gcc/config/aarch64/aarch64.h b/gcc/config/aarch64/aarch64.h
+index 1ce23c6..c21015f 100644
+--- a/gcc/config/aarch64/aarch64.h
++++ b/gcc/config/aarch64/aarch64.h
+@@ -281,6 +281,7 @@ extern unsigned aarch64_architecture_version;
+ #define AARCH64_ISA_F32MM (aarch64_isa_flags & AARCH64_FL_F32MM)
+ #define AARCH64_ISA_F64MM (aarch64_isa_flags & AARCH64_FL_F64MM)
+ #define AARCH64_ISA_BF16 (aarch64_isa_flags & AARCH64_FL_BF16)
++#define AARCH64_ISA_SB (aarch64_isa_flags & AARCH64_FL_SB)
+
+ /* Crypto is an optional extension to AdvSIMD. */
+ #define TARGET_CRYPTO (TARGET_SIMD && AARCH64_ISA_CRYPTO)
+@@ -378,6 +379,9 @@ extern unsigned aarch64_architecture_version;
+ #define TARGET_FIX_ERR_A53_835769_DEFAULT 1
+ #endif
+
++/* SB instruction is enabled through +sb. */
++#define TARGET_SB (AARCH64_ISA_SB)
++
+ /* Apply the workaround for Cortex-A53 erratum 835769. */
+ #define TARGET_FIX_ERR_A53_835769 \
+ ((aarch64_fix_a53_err835769 == 2) \
+@@ -1058,8 +1062,10 @@ typedef struct
+
+ #define RETURN_ADDR_RTX aarch64_return_addr
+
+-/* BTI c + 3 insns + 2 pointer-sized entries. */
+-#define TRAMPOLINE_SIZE (TARGET_ILP32 ? 24 : 32)
++/* BTI c + 3 insns
++ + sls barrier of DSB + ISB.
++ + 2 pointer-sized entries. */
++#define TRAMPOLINE_SIZE (24 + (TARGET_ILP32 ? 8 : 16))
+
+ /* Trampolines contain dwords, so must be dword aligned. */
+ #define TRAMPOLINE_ALIGNMENT 64
+diff --git a/gcc/config/aarch64/aarch64.md b/gcc/config/aarch64/aarch64.md
+index 8c8be3c..dda04ee 100644
+--- a/gcc/config/aarch64/aarch64.md
++++ b/gcc/config/aarch64/aarch64.md
+@@ -407,10 +407,25 @@
+ ;; Attribute that specifies whether the alternative uses MOVPRFX.
+ (define_attr "movprfx" "no,yes" (const_string "no"))
+
++;; Attribute to specify that an alternative has the length of a single
++;; instruction plus a speculation barrier.
++(define_attr "sls_length" "none,retbr,casesi" (const_string "none"))
++
+ (define_attr "length" ""
+ (cond [(eq_attr "movprfx" "yes")
+ (const_int 8)
+- ] (const_int 4)))
++
++ (eq_attr "sls_length" "retbr")
++ (cond [(match_test "!aarch64_harden_sls_retbr_p ()") (const_int 4)
++ (match_test "TARGET_SB") (const_int 8)]
++ (const_int 12))
++
++ (eq_attr "sls_length" "casesi")
++ (cond [(match_test "!aarch64_harden_sls_retbr_p ()") (const_int 16)
++ (match_test "TARGET_SB") (const_int 20)]
++ (const_int 24))
++ ]
++ (const_int 4)))
+
+ ;; Strictly for compatibility with AArch32 in pipeline models, since AArch64 has
+ ;; no predicated insns.
+@@ -447,8 +462,12 @@
+ (define_insn "indirect_jump"
+ [(set (pc) (match_operand:DI 0 "register_operand" "r"))]
+ ""
+- "br\\t%0"
+- [(set_attr "type" "branch")]
++ {
++ output_asm_insn ("br\\t%0", operands);
++ return aarch64_sls_barrier (aarch64_harden_sls_retbr_p ());
++ }
++ [(set_attr "type" "branch")
++ (set_attr "sls_length" "retbr")]
+ )
+
+ (define_insn "jump"
+@@ -765,7 +784,7 @@
+ "*
+ return aarch64_output_casesi (operands);
+ "
+- [(set_attr "length" "16")
++ [(set_attr "sls_length" "casesi")
+ (set_attr "type" "branch")]
+ )
+
+@@ -844,18 +863,23 @@
+ [(return)]
+ ""
+ {
++ const char *ret = NULL;
+ if (aarch64_return_address_signing_enabled ()
+ && TARGET_ARMV8_3
+ && !crtl->calls_eh_return)
+ {
+ if (aarch64_ra_sign_key == AARCH64_KEY_B)
+- return "retab";
++ ret = "retab";
+ else
+- return "retaa";
++ ret = "retaa";
+ }
+- return "ret";
++ else
++ ret = "ret";
++ output_asm_insn (ret, operands);
++ return aarch64_sls_barrier (aarch64_harden_sls_retbr_p ());
+ }
+- [(set_attr "type" "branch")]
++ [(set_attr "type" "branch")
++ (set_attr "sls_length" "retbr")]
+ )
+
+ (define_expand "return"
+@@ -867,8 +891,12 @@
+ (define_insn "simple_return"
+ [(simple_return)]
+ ""
+- "ret"
+- [(set_attr "type" "branch")]
++ {
++ output_asm_insn ("ret", operands);
++ return aarch64_sls_barrier (aarch64_harden_sls_retbr_p ());
++ }
++ [(set_attr "type" "branch")
++ (set_attr "sls_length" "retbr")]
+ )
+
+ (define_insn "*cb<optab><mode>1"
+@@ -1066,10 +1094,16 @@
+ (unspec:DI [(match_operand:DI 2 "const_int_operand")] UNSPEC_CALLEE_ABI)
+ (return)]
+ "SIBLING_CALL_P (insn)"
+- "@
+- br\\t%0
+- b\\t%c0"
+- [(set_attr "type" "branch, branch")]
++ {
++ if (which_alternative == 0)
++ {
++ output_asm_insn ("br\\t%0", operands);
++ return aarch64_sls_barrier (aarch64_harden_sls_retbr_p ());
++ }
++ return "b\\t%c0";
++ }
++ [(set_attr "type" "branch, branch")
++ (set_attr "sls_length" "retbr,none")]
+ )
+
+ (define_insn "*sibcall_value_insn"
+@@ -1080,10 +1114,16 @@
+ (unspec:DI [(match_operand:DI 3 "const_int_operand")] UNSPEC_CALLEE_ABI)
+ (return)]
+ "SIBLING_CALL_P (insn)"
+- "@
+- br\\t%1
+- b\\t%c1"
+- [(set_attr "type" "branch, branch")]
++ {
++ if (which_alternative == 0)
++ {
++ output_asm_insn ("br\\t%1", operands);
++ return aarch64_sls_barrier (aarch64_harden_sls_retbr_p ());
++ }
++ return "b\\t%c1";
++ }
++ [(set_attr "type" "branch, branch")
++ (set_attr "sls_length" "retbr,none")]
+ )
+
+ ;; Call subroutine returning any type.
+diff --git a/gcc/testsuite/gcc.target/aarch64/sls-mitigation/sls-miti-retbr-pacret.c b/gcc/testsuite/gcc.target/aarch64/sls-mitigation/sls-miti-retbr-pacret.c
+new file mode 100644
+index 0000000..fa1887a
+--- /dev/null
++++ b/gcc/testsuite/gcc.target/aarch64/sls-mitigation/sls-miti-retbr-pacret.c
+@@ -0,0 +1,21 @@
++/* Avoid ILP32 since pacret is only available for LP64 */
++/* { dg-do compile { target { ! ilp32 } } } */
++/* { dg-additional-options "-mharden-sls=retbr -mbranch-protection=pac-ret -march=armv8.3-a" } */
++
++/* Testing the do_return pattern for retaa and retab. */
++long retbr_subcall(void);
++long retbr_do_return_retaa(void)
++{
++ return retbr_subcall()+1;
++}
++
++__attribute__((target("branch-protection=pac-ret+b-key")))
++long retbr_do_return_retab(void)
++{
++ return retbr_subcall()+1;
++}
++
++/* Ensure there are no BR or RET instructions which are not directly followed
++ by a speculation barrier. */
++/* { dg-final { scan-assembler-not {\t(br|ret|retaa|retab)\tx[0-9][0-9]?\n\t(?!dsb\tsy\n\tisb)} } } */
++/* { dg-final { scan-assembler-not {ret\t} } } */
+diff --git a/gcc/testsuite/gcc.target/aarch64/sls-mitigation/sls-miti-retbr.c b/gcc/testsuite/gcc.target/aarch64/sls-mitigation/sls-miti-retbr.c
+new file mode 100644
+index 0000000..76b8d03
+--- /dev/null
++++ b/gcc/testsuite/gcc.target/aarch64/sls-mitigation/sls-miti-retbr.c
+@@ -0,0 +1,119 @@
++/* We ensure that -Wpedantic is off since it complains about the trampolines
++ we explicitly want to test. */
++/* { dg-additional-options "-mharden-sls=retbr -Wno-pedantic " } */
++/*
++ Ensure that the SLS hardening of RET and BR leaves no unprotected RET/BR
++ instructions.
++ */
++typedef int (foo) (int, int);
++typedef void (bar) (int, int);
++struct sls_testclass {
++ foo *x;
++ bar *y;
++ int left;
++ int right;
++};
++
++int
++retbr_sibcall_value_insn (struct sls_testclass x)
++{
++ return x.x(x.left, x.right);
++}
++
++void
++retbr_sibcall_insn (struct sls_testclass x)
++{
++ x.y(x.left, x.right);
++}
++
++/* Aim to test two different returns.
++ One that introduces a tail call in the middle of the function, and one that
++ has a normal return. */
++int
++retbr_multiple_returns (struct sls_testclass x)
++{
++ int temp;
++ if (x.left % 10)
++ return x.x(x.left, 100);
++ else if (x.right % 20)
++ {
++ return x.x(x.left * x.right, 100);
++ }
++ temp = x.left % x.right;
++ temp *= 100;
++ temp /= 2;
++ return temp % 3;
++}
++
++void
++retbr_multiple_returns_void (struct sls_testclass x)
++{
++ if (x.left % 10)
++ {
++ x.y(x.left, 100);
++ }
++ else if (x.right % 20)
++ {
++ x.y(x.left * x.right, 100);
++ }
++ return;
++}
++
++/* Testing the casesi jump via register. */
++__attribute__ ((optimize ("Os")))
++int
++retbr_casesi_dispatch (struct sls_testclass x)
++{
++ switch (x.left)
++ {
++ case -5:
++ return -2;
++ case -3:
++ return -1;
++ case 0:
++ return 0;
++ case 3:
++ return 1;
++ case 5:
++ break;
++ default:
++ __builtin_unreachable ();
++ }
++ return x.right;
++}
++
++/* Testing the BR in trampolines is mitigated against. */
++void f1 (void *);
++void f3 (void *, void (*)(void *));
++void f2 (void *);
++
++int
++retbr_trampolines (void *a, int b)
++{
++ if (!b)
++ {
++ f1 (a);
++ return 1;
++ }
++ if (b)
++ {
++ void retbr_tramp_internal (void *c)
++ {
++ if (c == a)
++ f2 (c);
++ }
++ f3 (a, retbr_tramp_internal);
++ }
++ return 0;
++}
++
++/* Testing the indirect_jump pattern. */
++void
++retbr_indirect_jump (int *buf)
++{
++ __builtin_longjmp(buf, 1);
++}
++
++/* Ensure there are no BR or RET instructions which are not directly followed
++ by a speculation barrier. */
++/* { dg-final { scan-assembler-not {\t(br|ret|retaa|retab)\tx[0-9][0-9]?\n\t(?!dsb\tsy\n\tisb|sb)} } } */
+diff --git a/gcc/testsuite/gcc.target/aarch64/sls-mitigation/sls-mitigation.exp b/gcc/testsuite/gcc.target/aarch64/sls-mitigation/sls-mitigation.exp
+new file mode 100644
+index 0000000..8122503
+--- /dev/null
++++ b/gcc/testsuite/gcc.target/aarch64/sls-mitigation/sls-mitigation.exp
+@@ -0,0 +1,73 @@
++# Regression driver for SLS mitigation on AArch64.
++# Copyright (C) 2020 Free Software Foundation, Inc.
++# Contributed by ARM Ltd.
++#
++# This file is part of GCC.
++#
++# GCC is free software; you can redistribute it and/or modify it
++# under the terms of the GNU General Public License as published by
++# the Free Software Foundation; either version 3, or (at your option)
++# any later version.
++#
++# GCC is distributed in the hope that it will be useful, but
++# WITHOUT ANY WARRANTY; without even the implied warranty of
++# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
++# General Public License for more details.
++#
++# You should have received a copy of the GNU General Public License
++# along with GCC; see the file COPYING3. If not see
++# <http://www.gnu.org/licenses/>. */
++
++# Exit immediately if this isn't an AArch64 target.
++if {![istarget aarch64*-*-*] } then {
++ return
++}
++
++# Load support procs.
++load_lib gcc-dg.exp
++load_lib torture-options.exp
++
++# If a testcase doesn't have special options, use these.
++global DEFAULT_CFLAGS
++if ![info exists DEFAULT_CFLAGS] then {
++ set DEFAULT_CFLAGS " "
++}
++
++# Initialize `dg'.
++dg-init
++torture-init
++
++# Use different architectures as well as the normal optimisation options.
++# (i.e. use both SB and DSB+ISB barriers).
++
++set save-dg-do-what-default ${dg-do-what-default}
++# Main loop.
++# Run with torture tests (i.e. a bunch of different optimisation levels) just
++# to increase test coverage.
++set dg-do-what-default assemble
++gcc-dg-runtest [lsort [glob -nocomplain $srcdir/$subdir/*.\[cCS\]]] \
++ "-save-temps" $DEFAULT_CFLAGS
++
++# Run the same tests but this time with SB extension.
++# Since not all supported assemblers will support that extension we decide
++# whether to assemble or just compile based on whether the extension is
++# supported for the available assembler.
++
++set templist {}
++foreach x $DG_TORTURE_OPTIONS {
++ lappend templist "$x -march=armv8.3-a+sb "
++ lappend templist "$x -march=armv8-a+sb "
++}
++set-torture-options $templist
++if { [check_effective_target_aarch64_asm_sb_ok] } {
++ set dg-do-what-default assemble
++} else {
++ set dg-do-what-default compile
++}
++gcc-dg-runtest [lsort [glob -nocomplain $srcdir/$subdir/*.\[cCS\]]] \
++ "-save-temps" $DEFAULT_CFLAGS
++set dg-do-what-default ${save-dg-do-what-default}
++
++# All done.
++torture-finish
++dg-finish
+diff --git a/gcc/testsuite/lib/target-supports.exp b/gcc/testsuite/lib/target-supports.exp
+index 8a186dd..9d2e093 100644
+--- a/gcc/testsuite/lib/target-supports.exp
++++ b/gcc/testsuite/lib/target-supports.exp
+@@ -9432,7 +9432,7 @@ proc check_effective_target_aarch64_tiny { } {
+ # various architecture extensions via the .arch_extension pseudo-op.
+
+ foreach { aarch64_ext } { "fp" "simd" "crypto" "crc" "lse" "dotprod" "sve"
+- "i8mm" "f32mm" "f64mm" "bf16" } {
++ "i8mm" "f32mm" "f64mm" "bf16" "sb" } {
+ eval [string map [list FUNC $aarch64_ext] {
+ proc check_effective_target_aarch64_asm_FUNC_ok { } {
+ if { [istarget aarch64*-*-*] } {
+--
+2.7.4
+
diff --git a/meta/recipes-devtools/gcc/gcc-10.1/0003-aarch64-Mitigate-SLS-for-BLR-instruction.patch b/meta/recipes-devtools/gcc/gcc-10.1/0003-aarch64-Mitigate-SLS-for-BLR-instruction.patch
new file mode 100644
index 0000000000..716a367172
--- /dev/null
+++ b/meta/recipes-devtools/gcc/gcc-10.1/0003-aarch64-Mitigate-SLS-for-BLR-instruction.patch
@@ -0,0 +1,658 @@
+Upstream-Status: Backport
+Signed-off-by: Ross Burton <ross.burton@arm.com>
+
+From a5e7efc40ed841934c1d913f39476afa17d8e5f7 Mon Sep 17 00:00:00 2001
+From: Matthew Malcomson <matthew.malcomson@arm.com>
+Date: Thu, 9 Jul 2020 09:11:59 +0100
+Subject: [PATCH 3/3] aarch64: Mitigate SLS for BLR instruction
+
+This patch introduces the mitigation for Straight Line Speculation past
+the BLR instruction.
+
+This mitigation replaces BLR instructions with a BL to a stub which uses
+a BR to jump to the original value. These function stubs are then
+appended with a speculation barrier to ensure no straight line
+speculation happens after these jumps.
+
+When optimising for speed we use a set of stubs for each function since
+this should help the branch predictor make more accurate predictions
+about where a stub should branch.
+
+When optimising for size we use one set of stubs for all functions.
+This set of stubs can have human readable names, and we are using
+`__call_indirect_x<N>` for register x<N>.
+
+When BTI branch protection is enabled the BLR instruction can jump to a
+`BTI c` instruction using any register, while the BR instruction can
+only jump to a `BTI c` instruction using the x16 or x17 registers.
+Hence, in order to ensure this transformation is safe we mov the value
+of the original register into x16 and use x16 for the BR.
+
+As an example when optimising for size:
+a
+ BLR x0
+instruction would get transformed to something like
+ BL __call_indirect_x0
+where __call_indirect_x0 labels a thunk that contains
+__call_indirect_x0:
+ MOV X16, X0
+ BR X16
+ <speculation barrier>
+
+The first version of this patch used local symbols specific to a
+compilation unit to try and avoid relocations.
+This was mistaken since functions coming from the same compilation unit
+can still be in different sections, and the assembler will insert
+relocations at jumps between sections.
+
+On any relocation the linker is permitted to emit a veneer to handle
+jumps between symbols that are very far apart. The registers x16 and
+x17 may be clobbered by these veneers.
+Hence the function stubs cannot rely on the values of x16 and x17 being
+the same as just before the function stub is called.
+
+Similar can be said for the hot/cold partitioning of single functions,
+so function-local stubs have the same restriction.
+
+This updated version of the patch never emits function stubs for x16 and
+x17, and instead forces other registers to be used.
+
+Given the above, there is now no benefit to local symbols (since they
+are not enough to avoid dealing with linker intricacies). This patch
+now uses global symbols with hidden visibility each stored in their own
+COMDAT section. This means stubs can be shared between compilation
+units while still avoiding the PLT indirection.
+
+This patch also removes the `__call_indirect_x30` stub (and
+function-local equivalent) which would simply jump back to the original
+location.
+
+The function-local stubs are emitted to the assembly output file in one
+chunk, which means we need not add the speculation barrier directly
+after each one.
+This is because we know for certain that the instructions directly after
+the BR in all but the last function stub will be from another one of
+these stubs and hence will not contain a speculation gadget.
+Instead we add a speculation barrier at the end of the sequence of
+stubs.
+
+The global stubs are emitted in COMDAT/.linkonce sections by
+themselves so that the linker can remove duplicates from multiple object
+files. This means they are not emitted in one chunk, and each one must
+include the speculation barrier.
+
+Another difference is that since the global stubs are shared across
+compilation units we do not know that all functions will be targeting an
+architecture supporting the SB instruction.
+Rather than provide multiple stubs for each architecture, we provide a
+stub that will work for all architectures -- using the DSB+ISB barrier.
+
+This mitigation does not apply for BLR instructions in the following
+places:
+- Some accesses to thread-local variables use a code sequence with a BLR
+ instruction. This code sequence is part of the binary interface between
+ compiler and linker. If this BLR instruction needs to be mitigated, it'd
+ probably be best to do so in the linker. It seems that the code sequence
+ for thread-local variable access is unlikely to lead to a Spectre Revalation
+ Gadget.
+- PLT stubs are produced by the linker and each contain a BLR instruction.
+ It seems that at most only after the last PLT stub a Spectre Revalation
+ Gadget might appear.
+
+Testing:
+ Bootstrap and regtest on AArch64
+ (with BOOT_CFLAGS="-mharden-sls=retbr,blr")
+ Used a temporary hack(1) in gcc-dg.exp to use these options on every
+ test in the testsuite, a slight modification to emit the speculation
+ barrier after every function stub, and a script to check that the
+ output never emitted a BLR, or unmitigated BR or RET instruction.
+ Similar on an aarch64-none-elf cross-compiler.
+
+1) Temporary hack emitted a speculation barrier at the end of every stub
+function, and used a script to ensure that:
+ a) Every RET or BR is immediately followed by a speculation barrier.
+ b) No BLR instruction is emitted by compiler.
+
+gcc/ChangeLog:
+
+ * config/aarch64/aarch64-protos.h (aarch64_indirect_call_asm):
+ New declaration.
+ * config/aarch64/aarch64.c (aarch64_regno_regclass): Handle new
+ stub registers class.
+ (aarch64_class_max_nregs): Likewise.
+ (aarch64_register_move_cost): Likewise.
+ (aarch64_sls_shared_thunks): Global array to store stub labels.
+ (aarch64_sls_emit_function_stub): New.
+ (aarch64_create_blr_label): New.
+ (aarch64_sls_emit_blr_function_thunks): New.
+ (aarch64_sls_emit_shared_blr_thunks): New.
+ (aarch64_asm_file_end): New.
+ (aarch64_indirect_call_asm): New.
+ (TARGET_ASM_FILE_END): Use aarch64_asm_file_end.
+ (TARGET_ASM_FUNCTION_EPILOGUE): Use
+ aarch64_sls_emit_blr_function_thunks.
+ * config/aarch64/aarch64.h (STB_REGNUM_P): New.
+ (enum reg_class): Add STUB_REGS class.
+ (machine_function): Introduce `call_via` array for
+ function-local stub labels.
+ * config/aarch64/aarch64.md (*call_insn, *call_value_insn): Use
+ aarch64_indirect_call_asm to emit code when hardening BLR
+ instructions.
+ * config/aarch64/constraints.md (Ucr): New constraint
+ representing registers for indirect calls. Is GENERAL_REGS
+ usually, and STUB_REGS when hardening BLR instruction against
+ SLS.
+ * config/aarch64/predicates.md (aarch64_general_reg): STUB_REGS class
+ is also a general register.
+
+gcc/testsuite/ChangeLog:
+
+ * gcc.target/aarch64/sls-mitigation/sls-miti-blr-bti.c: New test.
+ * gcc.target/aarch64/sls-mitigation/sls-miti-blr.c: New test.
+---
+ gcc/config/aarch64/aarch64-protos.h | 1 +
+ gcc/config/aarch64/aarch64.c | 225 ++++++++++++++++++++-
+ gcc/config/aarch64/aarch64.h | 15 ++
+ gcc/config/aarch64/aarch64.md | 11 +-
+ gcc/config/aarch64/constraints.md | 9 +
+ gcc/config/aarch64/predicates.md | 3 +-
+ .../aarch64/sls-mitigation/sls-miti-blr-bti.c | 40 ++++
+ .../aarch64/sls-mitigation/sls-miti-blr.c | 33 +++
+ 8 files changed, 328 insertions(+), 9 deletions(-)
+ create mode 100644 gcc/testsuite/gcc.target/aarch64/sls-mitigation/sls-miti-blr-bti.c
+ create mode 100644 gcc/testsuite/gcc.target/aarch64/sls-mitigation/sls-miti-blr.c
+
+diff --git a/gcc/config/aarch64/aarch64-protos.h b/gcc/config/aarch64/aarch64-protos.h
+index ee0ffde..839f801 100644
+--- a/gcc/config/aarch64/aarch64-protos.h
++++ b/gcc/config/aarch64/aarch64-protos.h
+@@ -782,6 +782,7 @@ extern const atomic_ool_names aarch64_ool_ldeor_names;
+ tree aarch64_resolve_overloaded_builtin_general (location_t, tree, void *);
+
+ const char *aarch64_sls_barrier (int);
++const char *aarch64_indirect_call_asm (rtx);
+ extern bool aarch64_harden_sls_retbr_p (void);
+ extern bool aarch64_harden_sls_blr_p (void);
+
+diff --git a/gcc/config/aarch64/aarch64.c b/gcc/config/aarch64/aarch64.c
+index 2389d49..0f7bba3 100644
+--- a/gcc/config/aarch64/aarch64.c
++++ b/gcc/config/aarch64/aarch64.c
+@@ -10605,6 +10605,9 @@ aarch64_label_mentioned_p (rtx x)
+ enum reg_class
+ aarch64_regno_regclass (unsigned regno)
+ {
++ if (STUB_REGNUM_P (regno))
++ return STUB_REGS;
++
+ if (GP_REGNUM_P (regno))
+ return GENERAL_REGS;
+
+@@ -10939,6 +10942,7 @@ aarch64_class_max_nregs (reg_class_t regclass, machine_mode mode)
+ unsigned int nregs, vec_flags;
+ switch (regclass)
+ {
++ case STUB_REGS:
+ case TAILCALL_ADDR_REGS:
+ case POINTER_REGS:
+ case GENERAL_REGS:
+@@ -13155,10 +13159,12 @@ aarch64_register_move_cost (machine_mode mode,
+ = aarch64_tune_params.regmove_cost;
+
+ /* Caller save and pointer regs are equivalent to GENERAL_REGS. */
+- if (to == TAILCALL_ADDR_REGS || to == POINTER_REGS)
++ if (to == TAILCALL_ADDR_REGS || to == POINTER_REGS
++ || to == STUB_REGS)
+ to = GENERAL_REGS;
+
+- if (from == TAILCALL_ADDR_REGS || from == POINTER_REGS)
++ if (from == TAILCALL_ADDR_REGS || from == POINTER_REGS
++ || from == STUB_REGS)
+ from = GENERAL_REGS;
+
+ /* Make RDFFR very expensive. In particular, if we know that the FFR
+@@ -22957,6 +22963,215 @@ aarch64_sls_barrier (int mitigation_required)
+ : "";
+ }
+
++static GTY (()) tree aarch64_sls_shared_thunks[30];
++static GTY (()) bool aarch64_sls_shared_thunks_needed = false;
++const char *indirect_symbol_names[30] = {
++ "__call_indirect_x0",
++ "__call_indirect_x1",
++ "__call_indirect_x2",
++ "__call_indirect_x3",
++ "__call_indirect_x4",
++ "__call_indirect_x5",
++ "__call_indirect_x6",
++ "__call_indirect_x7",
++ "__call_indirect_x8",
++ "__call_indirect_x9",
++ "__call_indirect_x10",
++ "__call_indirect_x11",
++ "__call_indirect_x12",
++ "__call_indirect_x13",
++ "__call_indirect_x14",
++ "__call_indirect_x15",
++ "", /* "__call_indirect_x16", */
++ "", /* "__call_indirect_x17", */
++ "__call_indirect_x18",
++ "__call_indirect_x19",
++ "__call_indirect_x20",
++ "__call_indirect_x21",
++ "__call_indirect_x22",
++ "__call_indirect_x23",
++ "__call_indirect_x24",
++ "__call_indirect_x25",
++ "__call_indirect_x26",
++ "__call_indirect_x27",
++ "__call_indirect_x28",
++ "__call_indirect_x29",
++};
++
++/* Function to create a BLR thunk. This thunk is used to mitigate straight
++ line speculation. Instead of a simple BLR that can be speculated past,
++ we emit a BL to this thunk, and this thunk contains a BR to the relevant
++ register. These thunks have the relevant speculation barries put after
++ their indirect branch so that speculation is blocked.
++
++ We use such a thunk so the speculation barriers are kept off the
++ architecturally executed path in order to reduce the performance overhead.
++
++ When optimizing for size we use stubs shared by the linked object.
++ When optimizing for performance we emit stubs for each function in the hope
++ that the branch predictor can better train on jumps specific for a given
++ function. */
++rtx
++aarch64_sls_create_blr_label (int regnum)
++{
++ gcc_assert (STUB_REGNUM_P (regnum));
++ if (optimize_function_for_size_p (cfun))
++ {
++ /* For the thunks shared between different functions in this compilation
++ unit we use a named symbol -- this is just for users to more easily
++ understand the generated assembly. */
++ aarch64_sls_shared_thunks_needed = true;
++ const char *thunk_name = indirect_symbol_names[regnum];
++ if (aarch64_sls_shared_thunks[regnum] == NULL)
++ {
++ /* Build a decl representing this function stub and record it for
++ later. We build a decl here so we can use the GCC machinery for
++ handling sections automatically (through `get_named_section` and
++ `make_decl_one_only`). That saves us a lot of trouble handling
++ the specifics of different output file formats. */
++ tree decl = build_decl (BUILTINS_LOCATION, FUNCTION_DECL,
++ get_identifier (thunk_name),
++ build_function_type_list (void_type_node,
++ NULL_TREE));
++ DECL_RESULT (decl) = build_decl (BUILTINS_LOCATION, RESULT_DECL,
++ NULL_TREE, void_type_node);
++ TREE_PUBLIC (decl) = 1;
++ TREE_STATIC (decl) = 1;
++ DECL_IGNORED_P (decl) = 1;
++ DECL_ARTIFICIAL (decl) = 1;
++ make_decl_one_only (decl, DECL_ASSEMBLER_NAME (decl));
++ resolve_unique_section (decl, 0, false);
++ aarch64_sls_shared_thunks[regnum] = decl;
++ }
++
++ return gen_rtx_SYMBOL_REF (Pmode, thunk_name);
++ }
++
++ if (cfun->machine->call_via[regnum] == NULL)
++ cfun->machine->call_via[regnum]
++ = gen_rtx_LABEL_REF (Pmode, gen_label_rtx ());
++ return cfun->machine->call_via[regnum];
++}
++
++/* Helper function for aarch64_sls_emit_blr_function_thunks and
++ aarch64_sls_emit_shared_blr_thunks below. */
++static void
++aarch64_sls_emit_function_stub (FILE *out_file, int regnum)
++{
++ /* Save in x16 and branch to that function so this transformation does
++ not prevent jumping to `BTI c` instructions. */
++ asm_fprintf (out_file, "\tmov\tx16, x%d\n", regnum);
++ asm_fprintf (out_file, "\tbr\tx16\n");
++}
++
++/* Emit all BLR stubs for this particular function.
++ Here we emit all the BLR stubs needed for the current function. Since we
++ emit these stubs in a consecutive block we know there will be no speculation
++ gadgets between each stub, and hence we only emit a speculation barrier at
++ the end of the stub sequences.
++
++ This is called in the TARGET_ASM_FUNCTION_EPILOGUE hook. */
++void
++aarch64_sls_emit_blr_function_thunks (FILE *out_file)
++{
++ if (! aarch64_harden_sls_blr_p ())
++ return;
++
++ bool any_functions_emitted = false;
++ /* We must save and restore the current function section since this assembly
++ is emitted at the end of the function. This means it can be emitted *just
++ after* the cold section of a function. That cold part would be emitted in
++ a different section. That switch would trigger a `.cfi_endproc` directive
++ to be emitted in the original section and a `.cfi_startproc` directive to
++ be emitted in the new section. Switching to the original section without
++ restoring would mean that the `.cfi_endproc` emitted as a function ends
++ would happen in a different section -- leaving an unmatched
++ `.cfi_startproc` in the cold text section and an unmatched `.cfi_endproc`
++ in the standard text section. */
++ section *save_text_section = in_section;
++ switch_to_section (function_section (current_function_decl));
++ for (int regnum = 0; regnum < 30; ++regnum)
++ {
++ rtx specu_label = cfun->machine->call_via[regnum];
++ if (specu_label == NULL)
++ continue;
++
++ targetm.asm_out.print_operand (out_file, specu_label, 0);
++ asm_fprintf (out_file, ":\n");
++ aarch64_sls_emit_function_stub (out_file, regnum);
++ any_functions_emitted = true;
++ }
++ if (any_functions_emitted)
++ /* Can use the SB if needs be here, since this stub will only be used
++ by the current function, and hence for the current target. */
++ asm_fprintf (out_file, "\t%s\n", aarch64_sls_barrier (true));
++ switch_to_section (save_text_section);
++}
++
++/* Emit shared BLR stubs for the current compilation unit.
++ Over the course of compiling this unit we may have converted some BLR
++ instructions to a BL to a shared stub function. This is where we emit those
++ stub functions.
++ This function is for the stubs shared between different functions in this
++ compilation unit. We share when optimizing for size instead of speed.
++
++ This function is called through the TARGET_ASM_FILE_END hook. */
++void
++aarch64_sls_emit_shared_blr_thunks (FILE *out_file)
++{
++ if (! aarch64_sls_shared_thunks_needed)
++ return;
++
++ for (int regnum = 0; regnum < 30; ++regnum)
++ {
++ tree decl = aarch64_sls_shared_thunks[regnum];
++ if (!decl)
++ continue;
++
++ const char *name = indirect_symbol_names[regnum];
++ switch_to_section (get_named_section (decl, NULL, 0));
++ ASM_OUTPUT_ALIGN (out_file, 2);
++ targetm.asm_out.globalize_label (out_file, name);
++ /* Only emits if the compiler is configured for an assembler that can
++ handle visibility directives. */
++ targetm.asm_out.assemble_visibility (decl, VISIBILITY_HIDDEN);
++ ASM_OUTPUT_TYPE_DIRECTIVE (out_file, name, "function");
++ ASM_OUTPUT_LABEL (out_file, name);
++ aarch64_sls_emit_function_stub (out_file, regnum);
++ /* Use the most conservative target to ensure it can always be used by any
++ function in the translation unit. */
++ asm_fprintf (out_file, "\tdsb\tsy\n\tisb\n");
++ ASM_DECLARE_FUNCTION_SIZE (out_file, name, decl);
++ }
++}
++
++/* Implement TARGET_ASM_FILE_END. */
++void
++aarch64_asm_file_end ()
++{
++ aarch64_sls_emit_shared_blr_thunks (asm_out_file);
++ /* Since this function will be called for the ASM_FILE_END hook, we ensure
++ that what would be called otherwise (e.g. `file_end_indicate_exec_stack`
++ for FreeBSD) still gets called. */
++#ifdef TARGET_ASM_FILE_END
++ TARGET_ASM_FILE_END ();
++#endif
++}
++
++const char *
++aarch64_indirect_call_asm (rtx addr)
++{
++ gcc_assert (REG_P (addr));
++ if (aarch64_harden_sls_blr_p ())
++ {
++ rtx stub_label = aarch64_sls_create_blr_label (REGNO (addr));
++ output_asm_insn ("bl\t%0", &stub_label);
++ }
++ else
++ output_asm_insn ("blr\t%0", &addr);
++ return "";
++}
++
+ /* Target-specific selftests. */
+
+ #if CHECKING_P
+@@ -23507,6 +23722,12 @@ aarch64_libgcc_floating_mode_supported_p
+ #undef TARGET_MD_ASM_ADJUST
+ #define TARGET_MD_ASM_ADJUST arm_md_asm_adjust
+
++#undef TARGET_ASM_FILE_END
++#define TARGET_ASM_FILE_END aarch64_asm_file_end
++
++#undef TARGET_ASM_FUNCTION_EPILOGUE
++#define TARGET_ASM_FUNCTION_EPILOGUE aarch64_sls_emit_blr_function_thunks
++
+ struct gcc_target targetm = TARGET_INITIALIZER;
+
+ #include "gt-aarch64.h"
+diff --git a/gcc/config/aarch64/aarch64.h b/gcc/config/aarch64/aarch64.h
+index 8e0fc37..7331450 100644
+--- a/gcc/config/aarch64/aarch64.h
++++ b/gcc/config/aarch64/aarch64.h
+@@ -643,6 +643,16 @@ extern unsigned aarch64_architecture_version;
+ #define GP_REGNUM_P(REGNO) \
+ (((unsigned) (REGNO - R0_REGNUM)) <= (R30_REGNUM - R0_REGNUM))
+
++/* Registers known to be preserved over a BL instruction. This consists of the
++ GENERAL_REGS without x16, x17, and x30. The x30 register is changed by the
++ BL instruction itself, while the x16 and x17 registers may be used by
++ veneers which can be inserted by the linker. */
++#define STUB_REGNUM_P(REGNO) \
++ (GP_REGNUM_P (REGNO) \
++ && (REGNO) != R16_REGNUM \
++ && (REGNO) != R17_REGNUM \
++ && (REGNO) != R30_REGNUM) \
++
+ #define FP_REGNUM_P(REGNO) \
+ (((unsigned) (REGNO - V0_REGNUM)) <= (V31_REGNUM - V0_REGNUM))
+
+@@ -667,6 +677,7 @@ enum reg_class
+ {
+ NO_REGS,
+ TAILCALL_ADDR_REGS,
++ STUB_REGS,
+ GENERAL_REGS,
+ STACK_REG,
+ POINTER_REGS,
+@@ -689,6 +700,7 @@ enum reg_class
+ { \
+ "NO_REGS", \
+ "TAILCALL_ADDR_REGS", \
++ "STUB_REGS", \
+ "GENERAL_REGS", \
+ "STACK_REG", \
+ "POINTER_REGS", \
+@@ -708,6 +720,7 @@ enum reg_class
+ { \
+ { 0x00000000, 0x00000000, 0x00000000 }, /* NO_REGS */ \
+ { 0x00030000, 0x00000000, 0x00000000 }, /* TAILCALL_ADDR_REGS */\
++ { 0x3ffcffff, 0x00000000, 0x00000000 }, /* STUB_REGS */ \
+ { 0x7fffffff, 0x00000000, 0x00000003 }, /* GENERAL_REGS */ \
+ { 0x80000000, 0x00000000, 0x00000000 }, /* STACK_REG */ \
+ { 0xffffffff, 0x00000000, 0x00000003 }, /* POINTER_REGS */ \
+@@ -862,6 +875,8 @@ typedef struct GTY (()) machine_function
+ struct aarch64_frame frame;
+ /* One entry for each hard register. */
+ bool reg_is_wrapped_separately[LAST_SAVED_REGNUM];
++ /* One entry for each general purpose register. */
++ rtx call_via[SP_REGNUM];
+ bool label_is_assembled;
+ } machine_function;
+ #endif
+diff --git a/gcc/config/aarch64/aarch64.md b/gcc/config/aarch64/aarch64.md
+index dda04ee..43da754 100644
+--- a/gcc/config/aarch64/aarch64.md
++++ b/gcc/config/aarch64/aarch64.md
+@@ -1022,16 +1022,15 @@
+ )
+
+ (define_insn "*call_insn"
+- [(call (mem:DI (match_operand:DI 0 "aarch64_call_insn_operand" "r, Usf"))
++ [(call (mem:DI (match_operand:DI 0 "aarch64_call_insn_operand" "Ucr, Usf"))
+ (match_operand 1 "" ""))
+ (unspec:DI [(match_operand:DI 2 "const_int_operand")] UNSPEC_CALLEE_ABI)
+ (clobber (reg:DI LR_REGNUM))]
+ ""
+ "@
+- blr\\t%0
++ * return aarch64_indirect_call_asm (operands[0]);
+ bl\\t%c0"
+- [(set_attr "type" "call, call")]
+-)
++ [(set_attr "type" "call, call")])
+
+ (define_expand "call_value"
+ [(parallel
+@@ -1050,13 +1049,13 @@
+
+ (define_insn "*call_value_insn"
+ [(set (match_operand 0 "" "")
+- (call (mem:DI (match_operand:DI 1 "aarch64_call_insn_operand" "r, Usf"))
++ (call (mem:DI (match_operand:DI 1 "aarch64_call_insn_operand" "Ucr, Usf"))
+ (match_operand 2 "" "")))
+ (unspec:DI [(match_operand:DI 3 "const_int_operand")] UNSPEC_CALLEE_ABI)
+ (clobber (reg:DI LR_REGNUM))]
+ ""
+ "@
+- blr\\t%1
++ * return aarch64_indirect_call_asm (operands[1]);
+ bl\\t%c1"
+ [(set_attr "type" "call, call")]
+ )
+diff --git a/gcc/config/aarch64/constraints.md b/gcc/config/aarch64/constraints.md
+index d993268..8cc6f50 100644
+--- a/gcc/config/aarch64/constraints.md
++++ b/gcc/config/aarch64/constraints.md
+@@ -24,6 +24,15 @@
+ (define_register_constraint "Ucs" "TAILCALL_ADDR_REGS"
+ "@internal Registers suitable for an indirect tail call")
+
++(define_register_constraint "Ucr"
++ "aarch64_harden_sls_blr_p () ? STUB_REGS : GENERAL_REGS"
++ "@internal Registers to be used for an indirect call.
++ This is usually the general registers, but when we are hardening against
++ Straight Line Speculation we disallow x16, x17, and x30 so we can use
++ indirection stubs. These indirection stubs cannot use the above registers
++ since they will be reached by a BL that may have to go through a linker
++ veneer.")
++
+ (define_register_constraint "w" "FP_REGS"
+ "Floating point and SIMD vector registers.")
+
+diff --git a/gcc/config/aarch64/predicates.md b/gcc/config/aarch64/predicates.md
+index 215fcec..1754b1e 100644
+--- a/gcc/config/aarch64/predicates.md
++++ b/gcc/config/aarch64/predicates.md
+@@ -32,7 +32,8 @@
+
+ (define_predicate "aarch64_general_reg"
+ (and (match_operand 0 "register_operand")
+- (match_test "REGNO_REG_CLASS (REGNO (op)) == GENERAL_REGS")))
++ (match_test "REGNO_REG_CLASS (REGNO (op)) == STUB_REGS
++ || REGNO_REG_CLASS (REGNO (op)) == GENERAL_REGS")))
+
+ ;; Return true if OP a (const_int 0) operand.
+ (define_predicate "const0_operand"
+diff --git a/gcc/testsuite/gcc.target/aarch64/sls-mitigation/sls-miti-blr-bti.c b/gcc/testsuite/gcc.target/aarch64/sls-mitigation/sls-miti-blr-bti.c
+new file mode 100644
+index 0000000..b1fb754
+--- /dev/null
++++ b/gcc/testsuite/gcc.target/aarch64/sls-mitigation/sls-miti-blr-bti.c
+@@ -0,0 +1,40 @@
++/* { dg-do compile } */
++/* { dg-additional-options "-mharden-sls=blr -mbranch-protection=bti" } */
++/*
++ Ensure that the SLS hardening of BLR leaves no BLR instructions.
++ Here we also check that there are no BR instructions with anything except an
++ x16 or x17 register. This is because a `BTI c` instruction can be branched
++ to using a BLR instruction using any register, but can only be branched to
++ with a BR using an x16 or x17 register.
++ */
++typedef int (foo) (int, int);
++typedef void (bar) (int, int);
++struct sls_testclass {
++ foo *x;
++ bar *y;
++ int left;
++ int right;
++};
++
++/* We test both RTL patterns for a call which returns a value and a call which
++ does not. */
++int blr_call_value (struct sls_testclass x)
++{
++ int retval = x.x(x.left, x.right);
++ if (retval % 10)
++ return 100;
++ return 9;
++}
++
++int blr_call (struct sls_testclass x)
++{
++ x.y(x.left, x.right);
++ if (x.left % 10)
++ return 100;
++ return 9;
++}
++
++/* { dg-final { scan-assembler-not {\tblr\t} } } */
++/* { dg-final { scan-assembler-not {\tbr\tx(?!16|17)} } } */
++/* { dg-final { scan-assembler {\tbr\tx(16|17)} } } */
++
+diff --git a/gcc/testsuite/gcc.target/aarch64/sls-mitigation/sls-miti-blr.c b/gcc/testsuite/gcc.target/aarch64/sls-mitigation/sls-miti-blr.c
+new file mode 100644
+index 0000000..88bafff
+--- /dev/null
++++ b/gcc/testsuite/gcc.target/aarch64/sls-mitigation/sls-miti-blr.c
+@@ -0,0 +1,33 @@
++/* { dg-additional-options "-mharden-sls=blr -save-temps" } */
++/* Ensure that the SLS hardening of BLR leaves no BLR instructions.
++ We only test that all BLR instructions have been removed, not that the
++ resulting code makes sense. */
++typedef int (foo) (int, int);
++typedef void (bar) (int, int);
++struct sls_testclass {
++ foo *x;
++ bar *y;
++ int left;
++ int right;
++};
++
++/* We test both RTL patterns for a call which returns a value and a call which
++ does not. */
++int blr_call_value (struct sls_testclass x)
++{
++ int retval = x.x(x.left, x.right);
++ if (retval % 10)
++ return 100;
++ return 9;
++}
++
++int blr_call (struct sls_testclass x)
++{
++ x.y(x.left, x.right);
++ if (x.left % 10)
++ return 100;
++ return 9;
++}
++
++/* { dg-final { scan-assembler-not {\tblr\t} } } */
++/* { dg-final { scan-assembler {\tbr\tx[0-9][0-9]?} } } */
+--
+2.7.4
+
--
2.26.2
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