On 2025-02-14 04:00, Stefano Stabellini wrote:
On Thu, 13 Feb 2025, Stefano Stabellini wrote:
> > diff --git a/xen/arch/x86/cpu/mcheck/mctelem.h
b/xen/arch/x86/cpu/mcheck/mctelem.h
> > index f4c5ff848d..2ccd490e5d 100644
> > --- a/xen/arch/x86/cpu/mcheck/mctelem.h
> > +++ b/xen/arch/x86/cpu/mcheck/mctelem.h
> > @@ -52,7 +52,7 @@
> > * the element from the processing list.
> > */
> >
> > -typedef struct mctelem_cookie *mctelem_cookie_t;
> > +typedef uint64_t *mctelem_cookie_t;
>
> Yet that makes it possible to de-reference the pointer. Which, as Andrew
> explained, is intended to be impossible. If this could be properly
> replaced (not exactly what Andrew indicated by "file it in /dev/null"),
> fine. Truly purging the code (i.e. as Andrew suggests) may still be an
> option, with appropriate justification. But simply adjusting the type
> and then moving on is too little, imo. Even if you used void * (to make
> de-referencing impossible) I'd view it as largely papering over an issue;
> then converting to other pointers (without explicit cast, and hence
> without making apparent the badness of doing so) would become possible.
What about converting to uintptr_t (not a pointer)?
In general, there are quite a few MISRA rules that we could mark as
blocking (clean) in our GitLab scan with just a few code changes like
this one. My goal is to make these rules blocking as soon as possible.
If I can improve the code in the process, that is even better, but it
is
not mandatory. And I would rather spend one more hour marking a second
rule as blocking instead.
What I mean is that I believe it would be acceptable to make some
compromises and accept non-perfect changes to the code if it helps us
enforce more rules as blocking in GitLab CI.
After briefly speaking with Andrew about this, and re-reading Jan's
email above, I think it is best to resolve this as a deviation.
Would this deviation work for you? Please suggest a better wording if
you prefer.
Nicola, in reality I think it would be better to use deviations.rst
because the SAF comment below would need to be replicated at every call
side, if I am not mistaken.
Would deviating macros "COOKIE2MCTE" and "MCTE2COOKIE" work?
In that case, that is a simple configuration tweak which then will be
justified in deviations.rst.
Thanks,
Nicola
diff --git a/docs/misra/safe.json b/docs/misra/safe.json
index b8a4f878ea..d9fbe959d1 100644
--- a/docs/misra/safe.json
+++ b/docs/misra/safe.json
@@ -92,6 +92,14 @@
},
{
"id": "SAF-11-safe",
+ "analyser": {
+ "eclair": "MC3A2.R11.2"
+ },
+ "name": "Rule 11.2: purposely impossible to dereference",
+ "text": "Certain pointers points to incomplete types
purposely so that they are impossible to dereference."
+ },
+ {
+ "id": "SAF-12-safe",
"analyser": {},
"name": "Sentinel",
"text": "Next ID to be used"
diff --git a/xen/arch/x86/cpu/mcheck/mctelem.h
b/xen/arch/x86/cpu/mcheck/mctelem.h
index f4c5ff848d..e845360c7d 100644
--- a/xen/arch/x86/cpu/mcheck/mctelem.h
+++ b/xen/arch/x86/cpu/mcheck/mctelem.h
@@ -52,6 +52,7 @@
* the element from the processing list.
*/
+/* SAF-11-safe: impossible to dereference */
typedef struct mctelem_cookie *mctelem_cookie_t;
typedef enum mctelem_class {
--
Nicola Vetrini, B.Sc.
Software Engineer
BUGSENG (https://bugseng.com)
LinkedIn: https://www.linkedin.com/in/nicola-vetrini-a42471253
