[clang] 839d974 - [DOCS] Add more detail to stack protector documentation
Peter Smith via cfe-commits
cfe-commits at lists.llvm.org
Thu Aug 6 05:59:23 PDT 2020
Author: Peter Smith
Date: 2020-08-06T13:47:21+01:00
New Revision: 839d974ee0e45f09b9665b4eed734ca1ba174d25
URL: https://github.com/llvm/llvm-project/commit/839d974ee0e45f09b9665b4eed734ca1ba174d25
DIFF: https://github.com/llvm/llvm-project/commit/839d974ee0e45f09b9665b4eed734ca1ba174d25.diff
LOG: [DOCS] Add more detail to stack protector documentation
The Clang -fstack-protector documentation mentions what functions are considered
vulnerable but does not mention the details of the implementation such as the use
of a global variable for the guard value. This brings the documentation more in
line with the GCC documentation at:
https://gcc.gnu.org/onlinedocs/gcc/Instrumentation-Options.html
and gives someone using the option more idea about what is protected.
This partly addresses https://bugs.llvm.org/show_bug.cgi?id=42764
Differential Revision: https://reviews.llvm.org/D85239
Added:
Modified:
clang/docs/ClangCommandLineReference.rst
clang/include/clang/Driver/Options.td
Removed:
################################################################################
diff --git a/clang/docs/ClangCommandLineReference.rst b/clang/docs/ClangCommandLineReference.rst
index 8eb010eae265..4caa08a82a72 100644
--- a/clang/docs/ClangCommandLineReference.rst
+++ b/clang/docs/ClangCommandLineReference.rst
@@ -2136,7 +2136,7 @@ Enable stack clash protection
.. option:: -fstack-protector, -fno-stack-protector
-Enable stack protectors for some functions vulnerable to stack smashing. This uses a loose heuristic which considers functions vulnerable if they contain a char (or 8bit integer) array or constant sized calls to alloca, which are of greater size than ssp-buffer-size (default: 8 bytes). All variable sized calls to alloca are considered vulnerable
+Enable stack protectors for some functions vulnerable to stack smashing. This uses a loose heuristic which considers functions vulnerable if they contain a char (or 8bit integer) array or constant sized calls to alloca , which are of greater size than ssp-buffer-size (default: 8 bytes). All variable sized calls to alloca are considered vulnerable. A function witha stack protector has a guard value added to the stack frame that is checked on function exit. The guard value must be positioned in the stack frame such that a buffer overflow from a vulnerable variable will overwrite the guard value before overwriting the function's return address. The reference stack guard value is stored in a global variable.
.. option:: -fstack-protector-all
diff --git a/clang/include/clang/Driver/Options.td b/clang/include/clang/Driver/Options.td
index 786a3c362842..fc31c23e4240 100644
--- a/clang/include/clang/Driver/Options.td
+++ b/clang/include/clang/Driver/Options.td
@@ -1801,10 +1801,15 @@ def fstack_protector_strong : Flag<["-"], "fstack-protector-strong">, Group<f_Gr
"as well as any calls to alloca or the taking of an address from a local variable">;
def fstack_protector : Flag<["-"], "fstack-protector">, Group<f_Group>,
HelpText<"Enable stack protectors for some functions vulnerable to stack smashing. "
- "This uses a loose heuristic which considers functions vulnerable "
- "if they contain a char (or 8bit integer) array or constant sized calls to "
- "alloca, which are of greater size than ssp-buffer-size (default: 8 bytes). "
- "All variable sized calls to alloca are considered vulnerable">;
+ "This uses a loose heuristic which considers functions vulnerable if they "
+ "contain a char (or 8bit integer) array or constant sized calls to alloca "
+ ", which are of greater size than ssp-buffer-size (default: 8 bytes). All "
+ "variable sized calls to alloca are considered vulnerable. A function with"
+ "a stack protector has a guard value added to the stack frame that is "
+ "checked on function exit. The guard value must be positioned in the "
+ "stack frame such that a buffer overflow from a vulnerable variable will "
+ "overwrite the guard value before overwriting the function's return "
+ "address. The reference stack guard value is stored in a global variable.">;
def ftrivial_auto_var_init : Joined<["-"], "ftrivial-auto-var-init=">, Group<f_Group>,
Flags<[CC1Option, CoreOption]>, HelpText<"Initialize trivial automatic stack variables: uninitialized (default)"
" | pattern">, Values<"uninitialized,pattern">;
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