From: Pavel Tatashin <pasha.tatashin@soleen.com>
To: Ard Biesheuvel <ardb@kernel.org>
Cc: Anshuman Khandual <anshuman.khandual@arm.com>,
Catalin Marinas <catalin.marinas@arm.com>,
James Morris <jmorris@namei.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Logan Gunthorpe <logang@deltatee.com>,
Tyler Hicks <tyhicks@linux.microsoft.com>,
Linux ARM <linux-arm-kernel@lists.infradead.org>,
Andrew Morton <akpm@linux-foundation.org>,
Will Deacon <will@kernel.org>, Mike Rapoport <rppt@kernel.org>
Subject: Re: [PATCH v2 1/1] arm64: mm: correct the inside linear map boundaries during hotplug check
Date: Mon, 15 Feb 2021 14:51:21 -0500 [thread overview]
Message-ID: <CA+CK2bDJ7Y2-vEpZrZ0fzigAfDgcJOmjhmin_GjTqioYXAYB3Q@mail.gmail.com> (raw)
In-Reply-To: <CAMj1kXESuD-von_dtzYcUMwK7TLF=qTki9bd8_iTo_isBwj13g@mail.gmail.com>
On Mon, Feb 15, 2021 at 2:34 PM Ard Biesheuvel <ardb@kernel.org> wrote:
>
> On Mon, 15 Feb 2021 at 20:30, Pavel Tatashin <pasha.tatashin@soleen.com> wrote:
> >
> > > Can't we simply use signed arithmetic here? This expression works fine
> > > if the quantities are all interpreted as s64 instead of u64
> >
> > I was thinking about that, but I do not like the idea of using sign
> > arithmetics for physical addresses. Also, I am worried that someone in
> > the future will unknowingly change it to unsigns or to phys_addr_t. It
> > is safer to have start explicitly set to 0 in case of wrap.
>
> memstart_addr is already a s64 for this exact reason.
memstart_addr is basically an offset and it must be negative. For
example, this would not work if it was not signed:
#define vmemmap ((struct page *)VMEMMAP_START - (memstart_addr >> PAGE_SHIFT))
However, on powerpc it is phys_addr_t type.
>
> Btw, the KASLR check is incorrect: memstart_addr could also be
> negative when running the 52-bit VA kernel on hardware that is only
> 48-bit VA capable.
Good point!
if (IS_ENABLED(CONFIG_ARM64_VA_BITS_52) && (vabits_actual != 52))
memstart_addr -= _PAGE_OFFSET(48) - _PAGE_OFFSET(52);
So, I will remove IS_ENABLED(CONFIG_RANDOMIZE_BASE) again.
I am OK to change start_linear_pa, end_linear_pa to signed, but IMO
what I have now is actually safer to make sure that does not break
again in the future.
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next prev parent reply other threads:[~2021-02-15 19:53 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-02-15 19:22 [PATCH v2 0/1] correct the inside linear map boundaries during hotplug check Pavel Tatashin
2021-02-15 19:22 ` [PATCH v2 1/1] arm64: mm: " Pavel Tatashin
2021-02-15 19:27 ` Ard Biesheuvel
2021-02-15 19:30 ` Pavel Tatashin
2021-02-15 19:34 ` Ard Biesheuvel
2021-02-15 19:51 ` Pavel Tatashin [this message]
2021-02-15 22:28 ` Pavel Tatashin
2021-02-16 3:12 ` Anshuman Khandual
2021-02-16 7:36 ` Ard Biesheuvel
2021-02-16 14:34 ` Pavel Tatashin
2021-02-16 2:55 ` Anshuman Khandual
2021-02-16 14:48 ` Pavel Tatashin
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