On 2025-03-24 13:50, Jan Beulich wrote:
On 18.03.2025 03:34, Volodymyr Babchuk wrote:
Both GCC and Clang support -fstack-protector feature, which add stack
canaries to functions where stack corruption is possible. This patch
makes general preparations to enable this feature on different
supported architectures:
- Added CONFIG_HAS_STACK_PROTECTOR option so each architecture
can enable this feature individually
- Added user-selectable CONFIG_STACK_PROTECTOR option
- Implemented code that sets up random stack canary and a basic
handler for stack protector failures
Stack guard value is initialized in two phases:
1. Pre-defined randomly-selected value.
2. Own implementation linear congruent random number generator. It
relies on get_cycles() being available very early. If get_cycles()
returns zero, it would leave pre-defined value from the previous
step.
[...]
+void asmlinkage __stack_chk_fail(void)
The use of asmlinkage here comes close to an abuse: The Misra deviation
is
about C code called from assembly code only. This isn't the case here;
instead
it's a function that the compiler generates calls to without source
code
explicitly saying so.
This imo wants approving from the Misra side as well, and even if
approved
likely requires a justifying code comment.
Here my suggestion would be an explicit deviation via a code comment, as
described in [1], to describe the motivation of introducing such
definition without a declaration. Moreover, asmlinkage is only relevant
for the missing declaration, but is not effective for other rules. It is
probably appropriate to mark the function "noreturn" as well, given its
purpose.
[1]
https://gitlab.com/xen-project/xen/-/blob/staging/docs/misra/documenting-violations.rst
--- /dev/null
+++ b/xen/include/xen/stack-protector.h
@@ -0,0 +1,39 @@
+#ifndef __XEN_STACK_PROTECTOR_H__
+#define __XEN_STACK_PROTECTOR_H__
+
+extern unsigned long __stack_chk_guard;
+
+/*
+ * This function should be called from a C function that escapes
stack
+ * canary tracking (by calling reset_stack_and_jump() for example).
+ */
+static always_inline void boot_stack_chk_guard_setup(void)
+{
+#ifdef CONFIG_STACK_PROTECTOR
+
+ /*
Nit: Hard tab slipped in.
Jan
--
Nicola Vetrini, B.Sc.
Software Engineer
BUGSENG (https://bugseng.com)
LinkedIn: https://www.linkedin.com/in/nicola-vetrini-a42471253
