From: Catalin Marinas <catalin.marinas@arm.com>
To: Luis Machado <luis.machado@linaro.org>
Cc: linux-arm-kernel@lists.infradead.org, linux-mm@kvack.org,
linux-arch@vger.kernel.org, Will Deacon <will@kernel.org>,
Dave P Martin <Dave.Martin@arm.com>,
Vincenzo Frascino <vincenzo.frascino@arm.com>,
Szabolcs Nagy <szabolcs.nagy@arm.com>,
Kevin Brodsky <kevin.brodsky@arm.com>,
Andrey Konovalov <andreyknvl@google.com>,
Peter Collingbourne <pcc@google.com>,
Andrew Morton <akpm@linux-foundation.org>,
Alan Hayward <Alan.Hayward@arm.com>,
Omair Javaid <omair.javaid@linaro.org>
Subject: Re: [PATCH v5 19/25] arm64: mte: Add PTRACE_{PEEK,POKE}MTETAGS support
Date: Fri, 3 Jul 2020 11:50:49 +0100 [thread overview]
Message-ID: <20200703104412.GB14950@gaia> (raw)
In-Reply-To: <7fd536af-f9fa-aa10-a4c3-001e80dd7d7b@linaro.org>
Hi Luis,
On Thu, Jun 25, 2020 at 02:10:10PM -0300, Luis Machado wrote:
> On 6/24/20 2:52 PM, Catalin Marinas wrote:
> > +/*
> > + * Access MTE tags in another process' address space as given in mm. Update
> > + * the number of tags copied. Return 0 if any tags copied, error otherwise.
> > + * Inspired by __access_remote_vm().
> > + */
> > +static int __access_remote_tags(struct task_struct *tsk, struct mm_struct *mm,
> > + unsigned long addr, struct iovec *kiov,
> > + unsigned int gup_flags)
> > +{
> > + struct vm_area_struct *vma;
> > + void __user *buf = kiov->iov_base;
> > + size_t len = kiov->iov_len;
> > + int ret;
> > + int write = gup_flags & FOLL_WRITE;
> > +
> > + if (!access_ok(buf, len))
> > + return -EFAULT;
> > +
> > + if (mmap_read_lock_killable(mm))
> > + return -EIO;
> > +
> > + while (len) {
> > + unsigned long tags, offset;
> > + void *maddr;
> > + struct page *page = NULL;
> > +
> > + ret = get_user_pages_remote(tsk, mm, addr, 1, gup_flags,
> > + &page, &vma, NULL);
> > + if (ret <= 0)
> > + break;
> > +
> > + /*
> > + * Only copy tags if the page has been mapped as PROT_MTE
> > + * (PG_mte_tagged set). Otherwise the tags are not valid and
> > + * not accessible to user. Moreover, an mprotect(PROT_MTE)
> > + * would cause the existing tags to be cleared if the page
> > + * was never mapped with PROT_MTE.
> > + */
> > + if (!test_bit(PG_mte_tagged, &page->flags)) {
> > + ret = -EOPNOTSUPP;
> > + put_page(page);
> > + break;
> > + }
[...]
> My understanding is that both the PEEKMTETAGS and POKEMTETAGS can
> potentially read/write less tags than requested, right? The iov_len field
> will be updated accordingly.
Yes.
(I missed this part due to the mix of top/bottom-posting)
> So the ptrace caller would need to loop and make sure all the tags were
> read/written, right?
Yes. As per the documentation patch, if the ptrace call returns 0,
iov_len is updated to the number of tags copied. The caller can retry
until it gets a negative return (error) or everything was copied.
> I'm considering the situation where the kernel reads/writes 0 tags (when
> requested to read/write 1 or more tags) an error we can't recover from. So
> this may indicate a page without PROT_MTE or an invalid address.
For this case, it should return -EOPNOTSUPP (see the documentation
patch; and, of course, also test the syscall in case I got anything
wrong).
--
Catalin
next prev parent reply other threads:[~2020-07-03 10:51 UTC|newest]
Thread overview: 46+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-06-24 17:52 [PATCH v5 00/25] arm64: Memory Tagging Extension user-space support Catalin Marinas
2020-06-24 17:52 ` [PATCH v5 01/25] arm64: mte: system register definitions Catalin Marinas
2020-06-24 17:52 ` [PATCH v5 02/25] arm64: mte: CPU feature detection and initial sysreg configuration Catalin Marinas
2020-06-24 17:52 ` [PATCH v5 03/25] arm64: mte: Use Normal Tagged attributes for the linear map Catalin Marinas
2020-06-24 17:52 ` [PATCH v5 04/25] arm64: mte: Add specific SIGSEGV codes Catalin Marinas
2020-06-24 17:52 ` [PATCH v5 05/25] arm64: mte: Handle synchronous and asynchronous tag check faults Catalin Marinas
2020-06-24 17:52 ` [PATCH v5 06/25] mm: Add PG_ARCH_2 page flag Catalin Marinas
2020-06-24 18:33 ` Andrew Morton
2020-06-24 18:36 ` Matthew Wilcox
2020-06-25 17:10 ` Catalin Marinas
2020-07-01 17:30 ` Catalin Marinas
2020-06-24 17:52 ` [PATCH v5 07/25] arm64: mte: Clear the tags when a page is mapped in user-space with PROT_MTE Catalin Marinas
2020-06-24 17:52 ` [PATCH v5 08/25] arm64: mte: Tags-aware copy_{user_,}highpage() implementations Catalin Marinas
2020-06-24 17:52 ` [PATCH v5 09/25] arm64: Avoid unnecessary clear_user_page() indirection Catalin Marinas
2020-06-24 17:52 ` [PATCH v5 10/25] arm64: mte: Tags-aware aware memcmp_pages() implementation Catalin Marinas
2020-06-24 17:52 ` [PATCH v5 11/25] mm: Introduce arch_calc_vm_flag_bits() Catalin Marinas
2020-06-24 18:36 ` Andrew Morton
2020-06-25 17:34 ` Catalin Marinas
2020-06-24 17:52 ` [PATCH v5 12/25] arm64: mte: Add PROT_MTE support to mmap() and mprotect() Catalin Marinas
2020-06-24 17:52 ` [PATCH v5 13/25] mm: Introduce arch_validate_flags() Catalin Marinas
2020-06-24 18:37 ` Andrew Morton
2020-06-24 17:52 ` [PATCH v5 14/25] arm64: mte: Validate the PROT_MTE request via arch_validate_flags() Catalin Marinas
2020-06-24 17:52 ` [PATCH v5 15/25] mm: Allow arm64 mmap(PROT_MTE) on RAM-based files Catalin Marinas
2020-06-24 18:42 ` Andrew Morton
2020-06-24 17:52 ` [PATCH v5 16/25] arm64: mte: Allow user control of the tag check mode via prctl() Catalin Marinas
2020-06-24 17:52 ` [PATCH v5 17/25] arm64: mte: Allow user control of the generated random tags " Catalin Marinas
2020-06-24 17:52 ` [PATCH v5 18/25] arm64: mte: Restore the GCR_EL1 register after a suspend Catalin Marinas
2020-06-24 17:52 ` [PATCH v5 19/25] arm64: mte: Add PTRACE_{PEEK,POKE}MTETAGS support Catalin Marinas
2020-06-25 17:10 ` Luis Machado
2020-07-01 17:16 ` Catalin Marinas
2020-07-01 17:32 ` Luis Machado
2020-07-03 13:18 ` Catalin Marinas
2020-07-03 10:50 ` Catalin Marinas [this message]
2020-06-24 17:52 ` [PATCH v5 20/25] fs: Handle intra-page faults in copy_mount_options() Catalin Marinas
2020-06-24 17:52 ` [PATCH v5 21/25] mm: Add arch hooks for saving/restoring tags Catalin Marinas
2020-06-24 18:45 ` Andrew Morton
2020-06-25 9:04 ` Steven Price
2020-06-25 12:09 ` Catalin Marinas
2020-06-24 17:52 ` [PATCH v5 22/25] arm64: mte: Enable swap of tagged pages Catalin Marinas
2020-06-25 11:37 ` Steven Price
2020-06-25 11:59 ` Catalin Marinas
2020-06-24 17:52 ` [PATCH v5 23/25] arm64: mte: Save tags when hibernating Catalin Marinas
2020-06-24 17:52 ` [PATCH v5 24/25] arm64: mte: Kconfig entry Catalin Marinas
2020-06-24 17:52 ` [PATCH v5 25/25] arm64: mte: Add Memory Tagging Extension documentation Catalin Marinas
2020-06-25 12:22 ` Szabolcs Nagy
2020-06-26 14:54 ` Catalin Marinas
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