From: Miles Chen <miles.chen@mediatek.com>
To: Vincenzo Frascino <vincenzo.frascino@arm.com>
Cc: Alexey Dobriyan <adobriyan@gmail.com>,
Andrew Morton <akpm@linux-foundation.org>,
<linux-kernel@vger.kernel.org>, <linux-fsdevel@vger.kernel.org>,
<linux-mediatek@lists.infradead.org>, <wsd_upstream@mediatek.com>,
Andrey Konovalov <andreyknvl@google.com>,
Alexander Potapenko <glider@google.com>,
Andrey Ryabinin <aryabinin@virtuozzo.com>,
Catalin Marinas <catalin.marinas@arm.com>,
Dmitry Vyukov <dvyukov@google.com>,
Marco Elver <elver@google.com>,
"Will Deacon" <will.deacon@arm.com>,
"Eric W . Biederman" <ebiederm@xmission.com>,
Song Bao Hua <song.bao.hua@hisilicon.com>,
<stable@vger.kernel.org>
Subject: Re: [PATCH v2] proc: use untagged_addr() for pagemap_read addresses
Date: Fri, 4 Dec 2020 09:33:10 +0800 [thread overview]
Message-ID: <1607045590.22275.6.camel@mtkswgap22> (raw)
In-Reply-To: <d836c2d2-321f-3931-568b-430d73c60c2c@arm.com>
On Thu, 2020-12-03 at 11:45 +0000, Vincenzo Frascino wrote:
> Hi Miles,
>
> On 11/27/20 5:07 AM, Miles Chen wrote:
> > When we try to visit the pagemap of a tagged userspace pointer, we find
> > that the start_vaddr is not correct because of the tag.
> > To fix it, we should untag the usespace pointers in pagemap_read().
> >
>
> Nit: s/usespace/userspace/ (please search and replace all occurrences :) )
>
> > I tested with 5.10-rc4 and the issue remains.
> >
> > Explaination from Catalin in [1]:
> >
>
> Nit: s/Explaination/Explanation/ (please search and replace all occurrences :) )
thanks, I will fix this and push v3
>
> > "
> > Arguably, that's a user-space bug since tagged file offsets were never
> > supported. In this case it's not even a tag at bit 56 as per the arm64
> > tagged address ABI but rather down to bit 47. You could say that the
> > problem is caused by the C library (malloc()) or whoever created the
> > tagged vaddr and passed it to this function. It's not a kernel
> > regression as we've never supported it.
> >
> > Now, pagemap is a special case where the offset is usually not generated
> > as a classic file offset but rather derived by shifting a user virtual
> > address. I guess we can make a concession for pagemap (only) and allow
> > such offset with the tag at bit (56 - PAGE_SHIFT + 3).
> > "
> >
> > My test code is baed on [2]:
>
> Nit: s/baed/based/ (please search and replace all occurrences :) )
thanks, I will fix this and push v3
Miles
>
> [...]
>
> > ---
> > fs/proc/task_mmu.c | 8 ++++++--
> > 1 file changed, 6 insertions(+), 2 deletions(-)
> >
> > diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
> > index 217aa2705d5d..92b277388f05 100644
> > --- a/fs/proc/task_mmu.c
> > +++ b/fs/proc/task_mmu.c
> > @@ -1599,11 +1599,15 @@ static ssize_t pagemap_read(struct file *file, char __user *buf,
> >
> > src = *ppos;
> > svpfn = src / PM_ENTRY_BYTES;
> > - start_vaddr = svpfn << PAGE_SHIFT;
> > end_vaddr = mm->task_size;
> >
> > /* watch out for wraparound */
> > - if (svpfn > mm->task_size >> PAGE_SHIFT)
> > + start_vaddr = end_vaddr;
> > + if (svpfn < (ULONG_MAX >> PAGE_SHIFT))
>
> It seems that 'svpfn' should be less-then-equal (<=) '(ULONG_MAX >>
> PAGE_SHIFT)'. Is there any specific reason why this is not the case?
>
> > + start_vaddr = untagged_addr(svpfn << PAGE_SHIFT);
> > +
> > + /* Ensure the address is inside the task */
> > + if (start_vaddr > mm->task_size)
> > start_vaddr = end_vaddr;
> >
> > /*
> >
>
> Otherwise:
>
> Reviewed-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
>
prev parent reply other threads:[~2020-12-04 1:34 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-11-27 5:07 [PATCH v2] proc: use untagged_addr() for pagemap_read addresses Miles Chen
2020-12-03 11:30 ` Catalin Marinas
2020-12-04 1:34 ` Miles Chen
2020-12-03 11:45 ` Vincenzo Frascino
2020-12-04 1:33 ` Miles Chen [this message]
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