Re: [tip: x86/urgent] x86/mm: Fix pti_clone_entry_text() for i386

Peter Zijlstra
2024-08-06T08:50:53Z

On Mon, Aug 05, 2024 at 09:52:06PM -0700, Guenter Roeck wrote:
> Hi Peter,
>
> On Thu, Aug 01, 2024 at 10:55:31AM -0000, tip-bot2 for Peter Zijlstra wrote:
> > The following commit has been merged into the x86/urgent branch of tip:
> >
> > Commit-ID: 49947e7aedfea2573bada0c95b85f6c2363bef9f
> > Gitweb: https://git.kernel.org/tip/49947e7aedfea2573bada0c95b85f6c2363bef9f
> > Author: Peter Zijlstra <peterz@infradead.org>
> > AuthorDate: Thu, 01 Aug 2024 12:42:25 +02:00
> > Committer: Peter Zijlstra <peterz@infradead.org>
> > CommitterDate: Thu, 01 Aug 2024 12:48:23 +02:00
> >
> > x86/mm: Fix pti_clone_entry_text() for i386
> >
> > While x86_64 has PMD aligned text sections, i386 does not have this
> > luxery. Notably ALIGN_ENTRY_TEXT_END is empty and _etext has PAGE
> > alignment.
> >
> > This means that text on i386 can be page granular at the tail end,
> > which in turn means that the PTI text clones should consistently
> > account for this.
> >
> > Make pti_clone_entry_text() consistent with pti_clone_kernel_text().
> >
> > Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
>
> With this patch in the tree, some of my qemu tests (those with PAE enabled)
> report several WARNING backtraces.
>
> WARNING: CPU: 0 PID: 1 at arch/x86/mm/pti.c:256 pti_clone_pgtable+0x298/0x2dc
>
> WARNING: CPU: 0 PID: 1 at arch/x86/mm/pti.c:394 pti_clone_pgtable+0x29a/0x2dc
>
> The backtraces are repeated multiple times.
>
> Please see
>
> https://kerneltests.org/builders/qemu-x86-master/builds/253/steps/qemubuildcommand/logs/stdio
>
> for complete logs.

Could you try the below patch? If that don't work, could you provide the
.config, I'm assuming that'll work with the bits I grabbed last time.

---
diff --git a/arch/x86/mm/pti.c b/arch/x86/mm/pti.c
index bfdf5f45b137..bec53f127c0d 100644
--- a/arch/x86/mm/pti.c
+++ b/arch/x86/mm/pti.c
@@ -634,14 +634,8 @@ void __init pti_init(void)
}
#endif

- pti_clone_user_shared();
-
/* Undo all global bits from the init pagetables in head_64.S: */
pti_set_kernel_image_nonglobal();
- /* Replace some of the global bits just for shared entry text: */
- pti_clone_entry_text();
- pti_setup_espfix64();
- pti_setup_vsyscall();
}

/*
@@ -659,7 +653,12 @@ void pti_finalize(void)
* We need to clone everything (again) that maps parts of the
* kernel image.
*/
+ pti_clone_user_shared();
+
pti_clone_entry_text();
+ pti_setup_espfix64();
+ pti_setup_vsyscall();
+
pti_clone_kernel_text();

debug_checkwx_user();