gcc7/gcc7-aarch64-sls-miti-1.patch

Backport to gcc7 of the below commit for bsc#1172798

commit 20da13e395bde597d8337167c712039c8f923c3b
Author: Matthew Malcomson <matthew.malcomson@arm.com>
Date:   Thu Jul 9 09:11:58 2020 +0100

    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.
    
    (cherry picked from commit a9ba2a9b77bec7eacaf066801f22d1c366a2bc86)
    
    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.

Index: gcc-7.5.0+r278197/gcc/config/aarch64/aarch64-protos.h
===================================================================
--- gcc-7.5.0+r278197.orig/gcc/config/aarch64/aarch64-protos.h
+++ gcc-7.5.0+r278197/gcc/config/aarch64/aarch64-protos.h
@@ -485,4 +485,7 @@ extern const atomic_ool_names aarch64_oo
 extern const atomic_ool_names aarch64_ool_ldclr_names;
 extern const atomic_ool_names aarch64_ool_ldeor_names;
 
+extern bool aarch64_harden_sls_retbr_p (void);
+extern bool aarch64_harden_sls_blr_p (void);
+
 #endif /* GCC_AARCH64_PROTOS_H */
Index: gcc-7.5.0+r278197/gcc/config/aarch64/aarch64.c
===================================================================
--- gcc-7.5.0+r278197.orig/gcc/config/aarch64/aarch64.c
+++ gcc-7.5.0+r278197/gcc/config/aarch64/aarch64.c
@@ -8814,6 +8814,79 @@ aarch64_validate_mcpu (const char *str,
   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);
+}
+
 /* Validate a command-line -march option.  Parse the arch and extensions
    (if any) specified in STR and throw errors if appropriate.  Put the
    results, if they are valid, in RES and ISA_FLAGS.  Return whether the
@@ -8930,6 +9003,9 @@ aarch64_override_options (void)
   selected_arch = NULL;
   selected_tune = NULL;
 
+  if (aarch64_harden_sls_string)
+    aarch64_validate_sls_mitigation (aarch64_harden_sls_string);
+
   /* -mcpu=CPU is shorthand for -march=ARCH_FOR_CPU, -mtune=CPU.
      If either of -march or -mtune is given, they override their
      respective component of -mcpu.  */
Index: gcc-7.5.0+r278197/gcc/config/aarch64/aarch64.opt
===================================================================
--- gcc-7.5.0+r278197.orig/gcc/config/aarch64/aarch64.opt
+++ gcc-7.5.0+r278197/gcc/config/aarch64/aarch64.opt
@@ -68,6 +68,10 @@ 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.
Index: gcc-7.5.0+r278197/gcc/doc/invoke.texi
===================================================================
--- gcc-7.5.0+r278197.orig/gcc/doc/invoke.texi
+++ gcc-7.5.0+r278197/gcc/doc/invoke.texi
@@ -589,6 +589,7 @@ Objective-C and Objective-C++ Dialects}.
 -mlow-precision-recip-sqrt  -mno-low-precision-recip-sqrt@gol
 -mlow-precision-sqrt  -mno-low-precision-sqrt@gol
 -mlow-precision-div  -mno-low-precision-div @gol
+-mharden-sls=@var{opts} @gol
 -march=@var{name}  -mcpu=@var{name}  -mtune=@var{name}}
 
 @emph{Adapteva Epiphany Options}
@@ -14143,6 +14144,17 @@ Permissible values are @samp{none}, whic
 functions, and @samp{all}, which enables pointer signing for all functions.  The
 default value is @samp{none}.
 
+@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.
+
 @end table
 
 @subsubsection @option{-march} and @option{-mcpu} Feature Modifiers