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From: Kees Cook <keescook@chromium.org>
To: Conor Dooley <conor@kernel.org>
Cc: Sami Tolvanen <samitolvanen@google.com>,
	Paul Walmsley <paul.walmsley@sifive.com>,
	Palmer Dabbelt <palmer@dabbelt.com>,
	Albert Ou <aou@eecs.berkeley.edu>,
	Andrew Morton <akpm@linux-foundation.org>,
	linux-mm@kvack.org, linux-riscv@lists.infradead.org,
	llvm@lists.linux.dev, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 2/2] riscv: mm: Update mmap_rnd_bits_max
Date: Sat, 30 Sep 2023 14:01:11 -0700	[thread overview]
Message-ID: <202309301400.4E1AD87@keescook> (raw)
In-Reply-To: <20230930-emporium-share-2bbdf7074e54@spud>

On Sat, Sep 30, 2023 at 10:02:35AM +0100, Conor Dooley wrote:
> On Fri, Sep 29, 2023 at 03:52:22PM -0700, Sami Tolvanen wrote:
> > On Fri, Sep 29, 2023 at 2:54 PM Kees Cook <keescook@chromium.org> wrote:
> > >
> > > On Fri, Sep 29, 2023 at 09:11:58PM +0000, Sami Tolvanen wrote:
> > > > ARCH_MMAP_RND_BITS_MAX is based on Sv39, which leaves a few
> > > > potential bits of mmap randomness on the table if we end up enabling
> > > > 4/5-level paging. Update mmap_rnd_bits_max to take the final address
> > > > space size into account. This increases mmap_rnd_bits_max from 24 to
> > > > 33 with Sv48/57.
> > > >
> > > > Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
> > >
> > > I like this. Is RISCV the only arch where the paging level can be chosen
> > > at boot time?
> > 
> > I haven't seen this elsewhere, but I also haven't looked at all the
> > other architectures that closely. arm64 does something interesting
> > with ARM64_VA_BITS_52, but I think we can still handle that in
> > Kconfig.
> 
> AFAIU, x86-64 can do this also:
> 
> 	no4lvl		[RISCV] Disable 4-level and 5-level paging modes. Forces
> 			kernel to use 3-level paging instead.
> 
> 	no5lvl		[X86-64,RISCV] Disable 5-level paging mode. Forces
> 			kernel to use 4-level paging instead.

Ah-ha! Okay, well, then let's track this idea:
https://github.com/KSPP/linux/issues/346


-- 
Kees Cook

_______________________________________________
linux-riscv mailing list
linux-riscv@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-riscv

WARNING: multiple messages have this Message-ID (diff)
From: Kees Cook <keescook@chromium.org>
To: Conor Dooley <conor@kernel.org>
Cc: Sami Tolvanen <samitolvanen@google.com>,
	Paul Walmsley <paul.walmsley@sifive.com>,
	Palmer Dabbelt <palmer@dabbelt.com>,
	Albert Ou <aou@eecs.berkeley.edu>,
	Andrew Morton <akpm@linux-foundation.org>,
	linux-mm@kvack.org, linux-riscv@lists.infradead.org,
	llvm@lists.linux.dev, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 2/2] riscv: mm: Update mmap_rnd_bits_max
Date: Sat, 30 Sep 2023 14:01:11 -0700	[thread overview]
Message-ID: <202309301400.4E1AD87@keescook> (raw)
In-Reply-To: <20230930-emporium-share-2bbdf7074e54@spud>

On Sat, Sep 30, 2023 at 10:02:35AM +0100, Conor Dooley wrote:
> On Fri, Sep 29, 2023 at 03:52:22PM -0700, Sami Tolvanen wrote:
> > On Fri, Sep 29, 2023 at 2:54 PM Kees Cook <keescook@chromium.org> wrote:
> > >
> > > On Fri, Sep 29, 2023 at 09:11:58PM +0000, Sami Tolvanen wrote:
> > > > ARCH_MMAP_RND_BITS_MAX is based on Sv39, which leaves a few
> > > > potential bits of mmap randomness on the table if we end up enabling
> > > > 4/5-level paging. Update mmap_rnd_bits_max to take the final address
> > > > space size into account. This increases mmap_rnd_bits_max from 24 to
> > > > 33 with Sv48/57.
> > > >
> > > > Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
> > >
> > > I like this. Is RISCV the only arch where the paging level can be chosen
> > > at boot time?
> > 
> > I haven't seen this elsewhere, but I also haven't looked at all the
> > other architectures that closely. arm64 does something interesting
> > with ARM64_VA_BITS_52, but I think we can still handle that in
> > Kconfig.
> 
> AFAIU, x86-64 can do this also:
> 
> 	no4lvl		[RISCV] Disable 4-level and 5-level paging modes. Forces
> 			kernel to use 3-level paging instead.
> 
> 	no5lvl		[X86-64,RISCV] Disable 5-level paging mode. Forces
> 			kernel to use 4-level paging instead.

Ah-ha! Okay, well, then let's track this idea:
https://github.com/KSPP/linux/issues/346


-- 
Kees Cook

  reply	other threads:[~2023-09-30 21:01 UTC|newest]

Thread overview: 30+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-09-29 21:11 [PATCH 0/2] riscv: Increase mmap_rnd_bits_max on Sv48/57 Sami Tolvanen
2023-09-29 21:11 ` Sami Tolvanen
2023-09-29 21:11 ` [PATCH 1/2] mm: Change mmap_rnd_bits_max to __ro_after_init Sami Tolvanen
2023-09-29 21:11   ` Sami Tolvanen
2023-09-29 21:55   ` Kees Cook
2023-09-29 21:55     ` Kees Cook
2023-09-29 21:11 ` [PATCH 2/2] riscv: mm: Update mmap_rnd_bits_max Sami Tolvanen
2023-09-29 21:11   ` Sami Tolvanen
2023-09-29 21:54   ` Kees Cook
2023-09-29 21:54     ` Kees Cook
2023-09-29 22:52     ` Sami Tolvanen
2023-09-29 22:52       ` Sami Tolvanen
2023-09-30  9:02       ` Conor Dooley
2023-09-30  9:02         ` Conor Dooley
2023-09-30 21:01         ` Kees Cook [this message]
2023-09-30 21:01           ` Kees Cook
2023-10-01 15:19           ` Pedro Falcato
2023-10-01 15:19             ` Pedro Falcato
2023-10-02  7:02             ` Alexandre Ghiti
2023-10-02  7:02               ` Alexandre Ghiti
2023-10-02 15:58               ` Sami Tolvanen
2023-10-02 15:58                 ` Sami Tolvanen
2023-12-06 13:14 ` [PATCH 0/2] riscv: Increase mmap_rnd_bits_max on Sv48/57 Palmer Dabbelt
2023-12-06 13:14   ` Palmer Dabbelt
2023-12-06 20:28   ` Kees Cook
2023-12-06 20:28     ` Kees Cook
2024-01-17 20:29   ` Sami Tolvanen
2024-01-17 20:29     ` Sami Tolvanen
2024-01-25 21:30 ` patchwork-bot+linux-riscv
2024-01-25 21:30   ` patchwork-bot+linux-riscv

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