Re: [PATCH v2 1/3] x86/mce: Avoid infinite loop for copy from user recovery
From: Borislav Petkov <bp@alien8.de>
Date: 2021-08-20 17:31:15
Also in:
linux-edac, lkml
Possibly related (same subject, not in this thread)
- 2021-01-14 · Re: [PATCH v2 1/3] x86/mce: Avoid infinite loop for copy from user recovery · "Luck, Tony" <tony.luck@intel.com>
- 2021-01-14 · Re: [PATCH v2 1/3] x86/mce: Avoid infinite loop for copy from user recovery · Borislav Petkov <bp@alien8.de>
- 2021-01-13 · Re: [PATCH v2 1/3] x86/mce: Avoid infinite loop for copy from user recovery · Borislav Petkov <bp@alien8.de>
- 2021-01-13 · RE: [PATCH v2 1/3] x86/mce: Avoid infinite loop for copy from user recovery · "Luck, Tony" <tony.luck@intel.com>
- 2021-01-13 · Re: [PATCH v2 1/3] x86/mce: Avoid infinite loop for copy from user recovery · Borislav Petkov <bp@alien8.de>
On Tue, Aug 17, 2021 at 05:29:40PM -0700, Tony Luck wrote:
quoted hunk ↗ jump to hunk
@@ -1287,17 +1291,34 @@ static void kill_me_maybe(struct callback_head *cb) } } -static void queue_task_work(struct mce *m, int kill_current_task) +static void queue_task_work(struct mce *m, char *msg, int kill_current_task) { - current->mce_addr = m->addr; - current->mce_kflags = m->kflags; - current->mce_ripv = !!(m->mcgstatus & MCG_STATUS_RIPV); - current->mce_whole_page = whole_page(m); + int count = ++current->mce_count; - if (kill_current_task) - current->mce_kill_me.func = kill_me_now; - else - current->mce_kill_me.func = kill_me_maybe; + /* First call, save all the details */ + if (count == 1) { + current->mce_addr = m->addr; + current->mce_kflags = m->kflags; + current->mce_ripv = !!(m->mcgstatus & MCG_STATUS_RIPV); + current->mce_whole_page = whole_page(m); + + if (kill_current_task) + current->mce_kill_me.func = kill_me_now; + else + current->mce_kill_me.func = kill_me_maybe; + } + + /* Ten is likley overkill. Don't expect more than two faults before task_work() */
"likely"
+ if (count > 10)
+ mce_panic("Too many machine checks while accessing user data", m, msg);Ok, aren't we too nasty here? Why should we panic the whole box even with 10 MCEs? It is still user memory... IOW, why not: if (count > 10) current->mce_kill_me.func = kill_me_now; and when we return, that user process dies immediately.
+ /* Second or later call, make sure page address matches the one from first call */
+ if (count > 1 && (current->mce_addr >> PAGE_SHIFT) != (m->addr >> PAGE_SHIFT))
+ mce_panic("Machine checks to different user pages", m, msg);
Same question here.
--
Regards/Gruss,
Boris.
https://people.kernel.org/tglx/notes-about-netiquette