commit 6427208ee82548346a2f42a8ac83fdd2f823fde2
Author: law <law@138bc75d-0d04-0410-961f-82ee72b054a4>
Date: Wed Sep 20 04:56:54 2017 +0000
* common.opt (-fstack-clash-protection): New option.
* flag-types.h (enum stack_check_type): Note difference between
-fstack-check= and -fstack-clash-protection.
* params.def (PARAM_STACK_CLASH_PROTECTION_GUARD_SIZE): New PARAM.
(PARAM_STACK_CLASH_PROTECTION_PROBE_INTERVAL): Likewise.
* toplev.c (process_options): Issue warnings/errors for cases
not handled with -fstack-clash-protection.
* doc/invoke.texi (-fstack-clash-protection): Document new option.
(-fstack-check): Note additional problem with -fstack-check=generic.
Note that -fstack-check is primarily for Ada and refer users
to -fstack-clash-protection for stack-clash-protection.
Document new params for stack clash protection.
* gcc.dg/stack-check-2.c: New test.
* lib/target-supports.exp
(check_effective_target_supports_stack_clash_protection): New function.
(check_effective_target_frame_pointer_for_non_leaf): Likewise.
(check_effective_target_caller_implicit_probes): Likewise.
git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@252994 138bc75d-0d04-0410-961f-82ee72b054a4
diff --git a/gcc/common.opt b/gcc/common.opt
index 16846c13b62..0c335cb12cd 100644
--- a/gcc/common.opt
+++ b/gcc/common.opt
@@ -1911,13 +1911,18 @@ Common Report Var(flag_variable_expansion_in_unroller) Optimization
Apply variable expansion when loops are unrolled
fstack-check=
-Common Report RejectNegative Joined
--fstack-check=[no|generic|specific] Insert stack checking code into the program
+Common Report RejectNegative Joined Optimization
+-fstack-check=[no|generic|specific] Insert stack checking code into the program.
fstack-check
Common Alias(fstack-check=, specific, no)
Insert stack checking code into the program. Same as -fstack-check=specific
+fstack-clash-protection
+Common Report Var(flag_stack_clash_protection) Optimization
+Insert code to probe each page of stack space as it is allocated to protect
+from stack-clash style attacks.
+
fstack-limit
Common Var(common_deferred_options) Defer
diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
index f7a15ca190e..313a6c5ff76 100644
--- a/gcc/doc/invoke.texi
+++ b/gcc/doc/invoke.texi
@@ -9406,6 +9406,21 @@ compilation for profile feedback and one for compilation without. The value
for compilation with profile feedback needs to be more conservative (higher) in
order to make tracer effective.
+@item stack-clash-protection-guard-size
+Specify the size of the operating system provided stack guard as
+2 raised to @var{num} bytes. The default value is 12 (4096 bytes).
+Acceptable values are between 12 and 30. Higher values may reduce the
+number of explicit probes, but a value larger than the operating system
+provided guard will leave code vulnerable to stack clash style attacks.
+
+@item stack-clash-protection-probe-interval
+Stack clash protection involves probing stack space as it is allocated. This
+param controls the maximum distance between probes into the stack as 2 raised
+to @var{num} bytes. Acceptable values are between 10 and 16 and defaults to
+12. Higher values may reduce the number of explicit probes, but a value
+larger than the operating system provided guard will leave code vulnerable to
+stack clash style attacks.
+
@item max-cse-path-length
The maximum number of basic blocks on path that CSE considers.
@@ -20949,7 +20964,8 @@ target support in the compiler but comes with the following drawbacks:
@enumerate
@item
Modified allocation strategy for large objects: they are always
-allocated dynamically if their size exceeds a fixed threshold.
+allocated dynamically if their size exceeds a fixed threshold. Note this
+may change the semantics of some code.
@item
Fixed limit on the size of the static frame of functions: when it is
@@ -20964,6 +20980,27 @@ generic implementation, code performance is hampered.
Note that old-style stack checking is also the fallback method for
@code{specific} if no target support has been added in the compiler.
+@samp{-fstack-check=} is designed for Ada's needs to detect infinite recursion
+and stack overflows. @samp{specific} is an excellent choice when compiling
+Ada code. It is not generally sufficient to protect against stack-clash
+attacks. To protect against those you want @samp{-fstack-clash-protection}.
+
+@item -fstack-clash-protection
+@opindex fstack-clash-protection
+Generate code to prevent stack clash style attacks. When this option is
+enabled, the compiler will only allocate one page of stack space at a time
+and each page is accessed immediately after allocation. Thus, it prevents
+allocations from jumping over any stack guard page provided by the
+operating system.
+
+Most targets do not fully support stack clash protection. However, on
+those targets @option{-fstack-clash-protection} will protect dynamic stack
+allocations. @option{-fstack-clash-protection} may also provide limited
+protection for static stack allocations if the target supports
+@option{-fstack-check=specific}.
+
+
+
@item -fstack-limit-register=@var{reg}
@itemx -fstack-limit-symbol=@var{sym}
@itemx -fno-stack-limit
diff --git a/gcc/flag-types.h b/gcc/flag-types.h
index 4fc5d33348e..21e943d38fa 100644
--- a/gcc/flag-types.h
+++ b/gcc/flag-types.h
@@ -139,7 +139,14 @@ enum excess_precision
EXCESS_PRECISION_STANDARD
};
-/* Type of stack check. */
+/* Type of stack check.
+
+ Stack checking is designed to detect infinite recursion and stack
+ overflows for Ada programs. Furthermore stack checking tries to ensure
+ in that scenario that enough stack space is left to run a signal handler.
+
+ -fstack-check= does not prevent stack-clash style attacks. For that
+ you want -fstack-clash-protection. */
enum stack_check_type
{
/* Do not check the stack. */
diff --git a/gcc/params.def b/gcc/params.def
index e51b847a7c4..e668624b0cb 100644
--- a/gcc/params.def
+++ b/gcc/params.def
@@ -208,6 +208,16 @@ DEFPARAM(PARAM_STACK_FRAME_GROWTH,
"Maximal stack frame growth due to inlining (in percent)",
1000, 0, 0)
+DEFPARAM(PARAM_STACK_CLASH_PROTECTION_GUARD_SIZE,
+ "stack-clash-protection-guard-size",
+ "Size of the stack guard expressed as a power of two.",
+ 12, 12, 30)
+
+DEFPARAM(PARAM_STACK_CLASH_PROTECTION_PROBE_INTERVAL,
+ "stack-clash-protection-probe-interval",
+ "Interval in which to probe the stack expressed as a power of two.",
+ 12, 10, 16)
+
/* The GCSE optimization will be disabled if it would require
significantly more memory than this value. */
DEFPARAM(PARAM_MAX_GCSE_MEMORY,
diff --git a/gcc/testsuite/gcc.dg/stack-check-2.c b/gcc/testsuite/gcc.dg/stack-check-2.c
new file mode 100644
index 00000000000..196c4bbfbdd
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/stack-check-2.c
@@ -0,0 +1,66 @@
+/* The goal here is to ensure that we never consider a call to a noreturn
+ function as a potential tail call.
+
+ Right now GCC discovers potential tail calls by looking at the
+ predecessors of the exit block. A call to a non-return function
+ has no successors and thus can never match that first filter.
+
+ But that could change one day and we want to catch it. The problem
+ is the compiler could potentially optimize a tail call to a nonreturn
+ function, even if the caller has a frame. That breaks the assumption
+ that calls probe *sp when saving the return address that some targets
+ depend on to elide stack probes. */
+
+/* { dg-do compile } */
+/* { dg-options "-O2 -fstack-clash-protection -fdump-tree-tailc -fdump-tree-optimized" } */
+/* { dg-require-effective-target supports_stack_clash_protection } */
+
+extern void foo (void) __attribute__ ((__noreturn__));
+
+
+void
+test_direct_1 (void)
+{
+ foo ();
+}
+
+void
+test_direct_2 (void)
+{
+ return foo ();
+}
+
+void (*indirect)(void)__attribute__ ((noreturn));
+
+
+void
+test_indirect_1 ()
+{
+ (*indirect)();
+}
+
+void
+test_indirect_2 (void)
+{
+ return (*indirect)();;
+}
+
+
+typedef void (*pvfn)() __attribute__ ((noreturn));
+
+void (*indirect_casted)(void);
+
+void
+test_indirect_casted_1 ()
+{
+ (*(pvfn)indirect_casted)();
+}
+
+void
+test_indirect_casted_2 (void)
+{
+ return (*(pvfn)indirect_casted)();
+}
+/* { dg-final { scan-tree-dump-not "tail call" "tailc" } } */
+/* { dg-final { scan-tree-dump-not "tail call" "optimized" } } */
+
diff --git a/gcc/testsuite/lib/target-supports.exp b/gcc/testsuite/lib/target-supports.exp
index ef371ad7efd..821cea9cb33 100644
--- a/gcc/testsuite/lib/target-supports.exp
+++ b/gcc/testsuite/lib/target-supports.exp
@@ -5392,3 +5392,95 @@ proc check_effective_target_fenv_exceptions {} {
}
} "-std=gnu99"]
}
+
+# Return 1 if the target supports the auto_inc_dec optimization pass.
+proc check_effective_target_autoincdec { } {
+ if { ![check_no_compiler_messages auto_incdec assembly { void f () { }
+ } "-O2 -fdump-rtl-auto_inc_dec" ] } {
+ return 0
+ }
+
+ set dumpfile [glob -nocomplain "auto_incdec[pid].c.\[0-9\]\[0-9\]\[0-9\]r.auto_inc_dec"]
+ if { [file exists $dumpfile ] } {
+ file delete $dumpfile
+ return 1
+ }
+ return 0
+}
+
+# Return 1 if the target has support for stack probing designed
+# to avoid stack-clash style attacks.
+#
+# This is used to restrict the stack-clash mitigation tests to
+# just those targets that have been explicitly supported.
+#
+# In addition to the prologue work on those targets, each target's
+# properties should be described in the functions below so that
+# tests do not become a mess of unreadable target conditions.
+#
+proc check_effective_target_supports_stack_clash_protection { } {
+
+ # Temporary until the target bits are fully ACK'd.
+# if { [istarget aarch*-*-*] || [istarget x86_64-*-*]
+# || [istarget i?86-*-*] || [istarget s390*-*-*]
+# || [istarget powerpc*-*-*] || [istarget rs6000*-*-*] } {
+# return 1
+# }
+ return 0
+}
+
+# Return 1 if the target creates a frame pointer for non-leaf functions
+# Note we ignore cases where we apply tail call optimization here.
+proc check_effective_target_frame_pointer_for_non_leaf { } {
+ if { [istarget aarch*-*-*] } {
+ return 1
+ }
+ return 0
+}
+
+# Return 1 if the target's calling sequence or its ABI
+# create implicit stack probes at or prior to function entry.
+proc check_effective_target_caller_implicit_probes { } {
+
+ # On x86/x86_64 the call instruction itself pushes the return
+ # address onto the stack. That is an implicit probe of *sp.
+ if { [istarget x86_64-*-*] || [istarget i?86-*-*] } {
+ return 1
+ }
+
+ # On PPC, the ABI mandates that the address of the outer
+ # frame be stored at *sp. Thus each allocation of stack
+ # space is itself an implicit probe of *sp.
+ if { [istarget powerpc*-*-*] || [istarget rs6000*-*-*] } {
+ return 1
+ }
+
+ # s390's ABI has a register save area allocated by the
+ # caller for use by the callee. The mere existence does
+ # not constitute a probe by the caller, but when the slots
+ # used by the callee those stores are implicit probes.
+ if { [istarget s390*-*-*] } {
+ return 1
+ }
+
+ # Not strictly true on aarch64, but we have agreed that we will
+ # consider any function that pushes SP more than 3kbytes into
+ # the guard page as broken. This essentially means that we can
+ # consider the aarch64 as having a caller implicit probe at
+ # *(sp + 1k).
+ if { [istarget aarch64*-*-*] } {
+ return 1;
+ }
+
+ return 0
+}
+
+# Targets that potentially realign the stack pointer often cause residual
+# stack allocations and make it difficult to elimination loops or residual
+# allocations for dynamic stack allocations
+proc check_effective_target_callee_realigns_stack { } {
+ if { [istarget x86_64-*-*] || [istarget i?86-*-*] } {
+ return 1
+ }
+ return 0
+}
diff --git a/gcc/toplev.c b/gcc/toplev.c
index 26f2ffb362c..1def163f8b9 100644
--- a/gcc/toplev.c
+++ b/gcc/toplev.c
@@ -1520,6 +1520,28 @@ process_options (void)
flag_associative_math = 0;
}
+#ifndef STACK_GROWS_DOWNWARD
+ /* -fstack-clash-protection is not currently supported on targets
+ where the stack grows up. */
+ if (flag_stack_clash_protection)
+ {
+ warning_at (UNKNOWN_LOCATION, 0,
+ "%<-fstack-clash-protection%> is not supported on targets "
+ "where the stack grows from lower to higher addresses");
+ flag_stack_clash_protection = 0;
+ }
+#endif
+
+ /* We can not support -fstack-check= and -fstack-clash-protection at
+ the same time. */
+ if (flag_stack_check != NO_STACK_CHECK && flag_stack_clash_protection)
+ {
+ warning_at (UNKNOWN_LOCATION, 0,
+ "%<-fstack-check=%> and %<-fstack-clash_protection%> are "
+ "mutually exclusive. Disabling %<-fstack-check=%>");
+ flag_stack_check = NO_STACK_CHECK;
+ }
+
/* With -fcx-limited-range, we do cheap and quick complex arithmetic. */
if (flag_cx_limited_range)
flag_complex_method = 0;