* [bug report] x86/mce: Mark fatal MCE's page as poison to avoid panic in the kdump kernel
@ 2023-10-25 5:44 Dan Carpenter
2023-10-25 6:19 ` Zhiquan Li
0 siblings, 1 reply; 3+ messages in thread
From: Dan Carpenter @ 2023-10-25 5:44 UTC (permalink / raw)
To: zhiquan1.li; +Cc: linux-edac
Hello Zhiquan Li,
The patch 1d11b153d23b: "x86/mce: Mark fatal MCE's page as poison to
avoid panic in the kdump kernel" from Oct 23, 2023 (linux-next),
leads to the following Smatch static checker warning:
arch/x86/kernel/cpu/mce/core.c:299 mce_panic()
error: we previously assumed 'final' could be null (see line 281)
arch/x86/kernel/cpu/mce/core.c
270 /* Now print uncorrected but with the final one last */
271 llist_for_each_entry(l, pending, llnode) {
272 struct mce *m = &l->mce;
273 if (!(m->status & MCI_STATUS_UC))
274 continue;
275 if (!final || mce_cmp(m, final)) {
276 print_mce(m);
277 if (!apei_err)
278 apei_err = apei_write_mce(m);
279 }
280 }
281 if (final) {
^^^^^
This assumes final can be NULL
282 print_mce(final);
283 if (!apei_err)
284 apei_err = apei_write_mce(final);
285 }
286 if (exp)
287 pr_emerg(HW_ERR "Machine check: %s\n", exp);
288 if (!fake_panic) {
289 if (panic_timeout == 0)
290 panic_timeout = mca_cfg.panic_timeout;
291
292 /*
293 * Kdump skips the poisoned page in order to avoid
294 * touching the error bits again. Poison the page even
295 * if the error is fatal and the machine is about to
296 * panic.
297 */
298 if (kexec_crash_loaded()) {
--> 299 p = pfn_to_online_page(final->addr >> PAGE_SHIFT);
^^^^^^^^^^^
Unchecked dereference
300 if (final && (final->status & MCI_STATUS_ADDRV) && p)
^^^^^
Checked too late
301 SetPageHWPoison(p);
302 }
303 panic(msg);
304 } else
305 pr_emerg(HW_ERR "Fake kernel panic: %s\n", msg);
306
307 out:
308 instrumentation_end();
309 }
regards,
dan carpenter
^ permalink raw reply [flat|nested] 3+ messages in thread* Re: [bug report] x86/mce: Mark fatal MCE's page as poison to avoid panic in the kdump kernel
2023-10-25 5:44 [bug report] x86/mce: Mark fatal MCE's page as poison to avoid panic in the kdump kernel Dan Carpenter
@ 2023-10-25 6:19 ` Zhiquan Li
2023-10-25 7:48 ` Borislav Petkov
0 siblings, 1 reply; 3+ messages in thread
From: Zhiquan Li @ 2023-10-25 6:19 UTC (permalink / raw)
To: Dan Carpenter; +Cc: linux-edac
On 2023/10/25 13:44, Dan Carpenter wrote:
> Hello Zhiquan Li,
>
> The patch 1d11b153d23b: "x86/mce: Mark fatal MCE's page as poison to
> avoid panic in the kdump kernel" from Oct 23, 2023 (linux-next),
> leads to the following Smatch static checker warning:
>
> arch/x86/kernel/cpu/mce/core.c:299 mce_panic()
> error: we previously assumed 'final' could be null (see line 281)
>
> arch/x86/kernel/cpu/mce/core.c
> 270 /* Now print uncorrected but with the final one last */
> 271 llist_for_each_entry(l, pending, llnode) {
> 272 struct mce *m = &l->mce;
> 273 if (!(m->status & MCI_STATUS_UC))
> 274 continue;
> 275 if (!final || mce_cmp(m, final)) {
> 276 print_mce(m);
> 277 if (!apei_err)
> 278 apei_err = apei_write_mce(m);
> 279 }
> 280 }
> 281 if (final) {
> ^^^^^
> This assumes final can be NULL
>
> 282 print_mce(final);
> 283 if (!apei_err)
> 284 apei_err = apei_write_mce(final);
> 285 }
> 286 if (exp)
> 287 pr_emerg(HW_ERR "Machine check: %s\n", exp);
> 288 if (!fake_panic) {
> 289 if (panic_timeout == 0)
> 290 panic_timeout = mca_cfg.panic_timeout;
> 291
> 292 /*
> 293 * Kdump skips the poisoned page in order to avoid
> 294 * touching the error bits again. Poison the page even
> 295 * if the error is fatal and the machine is about to
> 296 * panic.
> 297 */
> 298 if (kexec_crash_loaded()) {
> --> 299 p = pfn_to_online_page(final->addr >> PAGE_SHIFT);
> ^^^^^^^^^^^
> Unchecked dereference
>
> 300 if (final && (final->status & MCI_STATUS_ADDRV) && p)
> ^^^^^
> Checked too late
>
> 301 SetPageHWPoison(p);
Nice catch!
This part should be changed like these:
+ if (final && (final->status & MCI_STATUS_ADDRV))
+ p = pfn_to_online_page(final->addr >> PAGE_SHIFT);
+ if (p)
+ SetPageHWPoison(p);
The assignment can not be put into the "if" condition, checkpatch.pl script
will complain it. So it have to take a separate line.
I'll re-validate the patch and send V5 soon.
Thanks a lot, Dan.
Best Regards,
Zhiquan
> 302 }
> 303 panic(msg);
> 304 } else
> 305 pr_emerg(HW_ERR "Fake kernel panic: %s\n", msg);
> 306
> 307 out:
> 308 instrumentation_end();
> 309 }
>
> regards,
> dan carpenter
^ permalink raw reply [flat|nested] 3+ messages in thread* Re: [bug report] x86/mce: Mark fatal MCE's page as poison to avoid panic in the kdump kernel
2023-10-25 6:19 ` Zhiquan Li
@ 2023-10-25 7:48 ` Borislav Petkov
0 siblings, 0 replies; 3+ messages in thread
From: Borislav Petkov @ 2023-10-25 7:48 UTC (permalink / raw)
To: Zhiquan Li; +Cc: Dan Carpenter, linux-edac
On Wed, Oct 25, 2023 at 02:19:26PM +0800, Zhiquan Li wrote:
> + if (final && (final->status & MCI_STATUS_ADDRV))
> + p = pfn_to_online_page(final->addr >> PAGE_SHIFT);
> + if (p)
> + SetPageHWPoison(p);
>
> The assignment can not be put into the "if" condition, checkpatch.pl script
> will complain it.
It doesn't complain here:
$ git diff | ./scripts/checkpatch.pl
total: 0 errors, 0 warnings, 14 lines checked
Your patch has no obvious style problems and is ready for submission
> I'll re-validate the patch and send V5 soon.
When you do, please send it with my edits to the text.
Zapped from tip for now.
Thx.
--
Regards/Gruss,
Boris.
https://people.kernel.org/tglx/notes-about-netiquette
^ permalink raw reply [flat|nested] 3+ messages in thread
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2023-10-25 5:44 [bug report] x86/mce: Mark fatal MCE's page as poison to avoid panic in the kdump kernel Dan Carpenter
2023-10-25 6:19 ` Zhiquan Li
2023-10-25 7:48 ` Borislav Petkov
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