From: Song Liu <songliubraving@fb.com>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@kernel.org>,
"Peter Zijlstra (Intel)" <peterz@infradead.org>,
Linux List Kernel Mailing <linux-kernel@vger.kernel.org>,
the arch/x86 maintainers <x86@kernel.org>
Subject: Re: [GIT pull] x86/pti for 5.4-rc1
Date: Tue, 17 Sep 2019 23:28:38 +0000 [thread overview]
Message-ID: <E4AF8E4C-A307-4AE7-85AA-F579D5BFDBDD@fb.com> (raw)
In-Reply-To: <CAHk-=whbOhAmc3FEhnEkdM9AXFuKM+964r+uzzm_Q9qFaxTC7g@mail.gmail.com>
> On Sep 17, 2019, at 12:01 PM, Linus Torvalds <torvalds@linux-foundation.org> wrote:
>
> On Tue, Sep 17, 2019 at 11:49 AM Song Liu <songliubraving@fb.com> wrote:
>>
>> I guess we need something like the following?
>>
>> diff --git i/arch/x86/mm/pti.c w/arch/x86/mm/pti.c
>> index b196524759ec..7846916c3bcd 100644
>> --- i/arch/x86/mm/pti.c
>> +++ w/arch/x86/mm/pti.c
>> @@ -306,6 +306,8 @@ pti_clone_pgtable(unsigned long start, unsigned long end,
>> {
>> unsigned long addr;
>>
>> + if (WARN_ON_ONCE(start & ~PAGE_MASK))
>> + return;
>
> I don't think we ever care about the low bits of the address below the
> page mask, so this one probably wouldn't make any difference.
>
> To match the other cases, I'd make it just a plain
>
> WARN_ON_ONCE(start & ~PAGE_MASK));
>
> and leave it at that. The existing commit added the warning, but then
> just made the code work despite it all. I'd continue that same logic.
>
>> if (pmd_large(*pmd) || level == PTI_CLONE_PMD) {
>> + if (WARN_ON_ONCE(addr & ~PMD_MASK))
>> + return;
>> target_pmd = pti_user_pagetable_walk_pmd(addr);
>> if (WARN_ON(!target_pmd))
>> return;
>
> Again, I think to match the other cases, I'd just do
>
> - addr += PMD_SIZE;
> + WARN_ON_ONCE(addr & ~PMD_MASK);
> + addr = round_up(addr + 1, PMD_SIZE);
>
> which now admittedly clones too much, but _does_ clone the requested range.
>
> But maybe it really doesn't matter, since this condition just
> shouldn't happen in the first place.
>
> And arguably, the "clone more than requested" issue is true, and maybe
> your "warn and refuse to clone by returning" is the right thing to do.
>
> So I have very few strong opinions in this area, I just reacted to
> looking at the patch that it didn't seem to cover all the cases.
How about we just do:
diff --git i/arch/x86/mm/pti.c w/arch/x86/mm/pti.c
index b196524759ec..0437f65250db 100644
--- i/arch/x86/mm/pti.c
+++ w/arch/x86/mm/pti.c
@@ -341,6 +341,7 @@ pti_clone_pgtable(unsigned long start, unsigned long end,
}
if (pmd_large(*pmd) || level == PTI_CLONE_PMD) {
+ WARN_ON_ONCE(addr & ~PMD_MASK);
target_pmd = pti_user_pagetable_walk_pmd(addr);
if (WARN_ON(!target_pmd))
return;
So it is a "warn and continue" check just for unaligned PMD address.
Thanks,
Song
next prev parent reply other threads:[~2019-09-17 23:29 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-09-16 13:30 [GIT pull] irq/core for 5.4-rc1 Thomas Gleixner
2019-09-16 13:30 ` [GIT pull] x86/irq " Thomas Gleixner
2019-09-17 20:15 ` pr-tracker-bot
2019-09-16 13:30 ` [GIT pull] smp/hotplug " Thomas Gleixner
2019-09-17 20:15 ` pr-tracker-bot
2019-09-16 13:30 ` [GIT pull] x86/pti " Thomas Gleixner
2019-09-17 18:13 ` Linus Torvalds
2019-09-17 18:48 ` Song Liu
2019-09-17 19:01 ` Linus Torvalds
2019-09-17 23:28 ` Song Liu [this message]
2019-09-17 23:35 ` Linus Torvalds
2019-09-18 10:40 ` Song Liu
2019-09-25 6:23 ` Ingo Molnar
2019-09-17 20:15 ` pr-tracker-bot
2019-09-16 13:30 ` [GIT pull] timers/core " Thomas Gleixner
2019-09-17 20:15 ` pr-tracker-bot
2019-09-16 13:30 ` [GIT pull] timers/urgent " Thomas Gleixner
2019-09-17 20:15 ` pr-tracker-bot
2019-09-16 13:30 ` [GIT pull] x86/apic " Thomas Gleixner
2019-09-17 20:15 ` pr-tracker-bot
2019-09-17 20:15 ` [GIT pull] irq/core " pr-tracker-bot
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