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From: Will Deacon <will.deacon@arm.com>
To: Kees Cook <keescook@chromium.org>
Cc: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	Rob Herring <robh@kernel.org>,
	Laura Abbott <lauraa@codeaurora.org>,
	Leif Lindholm <leif.lindholm@linaro.org>,
	Stephen Boyd <sboyd@codeaurora.org>,
	"msalter@redhat.com" <msalter@redhat.com>,
	Rabin Vincent <rabin@rab.in>, Liu hua <sdu.liu@huawei.com>,
	Nikolay Borisov <Nikolay.Borisov@arm.com>,
	Nicolas Pitre <nicolas.pitre@linaro.org>,
	Tomasz Figa <t.figa@samsung.com>,
	Doug Anderson <dianders@google.com>,
	Jason Wessel <jason.wessel@windriver.com>,
	Catalin Marinas <Catalin.Marinas@arm.com>,
	Russell King - ARM Linux <linux@arm.linux.org.uk>,
	"linux-arm-kernel@lists.infradead.org" 
	<linux-arm-kernel@lists.infradead.org>,
	"linux-doc@vger.kernel.org" <linux-doc@vger.kernel.org>
Subject: Re: [PATCH v4 7/8] ARM: mm: allow non-text sections to be non-executable
Date: Tue, 26 Aug 2014 15:43:03 +0100	[thread overview]
Message-ID: <20140826144303.GX23445@arm.com> (raw)
In-Reply-To: <CAGXu5jLnXeavr4E4YF9jtB03iA-y4vLZjf83a8ABzUC-hdkz9w@mail.gmail.com>

On Wed, Aug 20, 2014 at 01:37:14PM +0100, Kees Cook wrote:
> On Tue, Aug 19, 2014 at 7:33 AM, Will Deacon <will.deacon@arm.com> wrote:
> > On Wed, Aug 13, 2014 at 06:06:32PM +0100, Kees Cook wrote:
> >> +/*
> >> + * Updates section permissions only for the current mm (sections are
> >> + * copied into each mm). During startup, this is the init_mm.
> >> + */
> >> +static inline void section_update(unsigned long addr, pmdval_t mask,
> >> +                               pmdval_t prot)
> >> +{
> >> +     struct mm_struct *mm;
> >> +     pmd_t *pmd;
> >> +
> >> +     mm = current->active_mm;
> >> +     pmd = pmd_offset(pud_offset(pgd_offset(mm, addr), addr), addr);
> >> +
> >> +#ifdef CONFIG_ARM_LPAE
> >> +     pmd[0] = __pmd((pmd_val(pmd[0]) & mask) | prot);
> >> +#else
> >> +     if (addr & SECTION_SIZE)
> >> +             pmd[1] = __pmd((pmd_val(pmd[1]) & mask) | prot);
> >> +     else
> >> +             pmd[0] = __pmd((pmd_val(pmd[0]) & mask) | prot);
> >> +#endif
> >> +     flush_pmd_entry(pmd);
> >> +     local_flush_tlb_kernel_range(addr, addr + SECTION_SIZE);
> >
> > Why only a local flush? You're changing global mappings here, right?
> 
> Yes, but with the a15 errata, it cannot use a global flush. As a
> result, section_update can only be used by a single CPU which is how
> the usage is managed. Perhaps I should add some comments to that
> effect? (There was a thread a few months ago on this problem and this
> shook out as a solution.)

Hmm, so do you mandate that preemption is disabled during sections of code
where the permissions must be changed after boot? (e.g. ftrace patching)

Will

WARNING: multiple messages have this Message-ID (diff)
From: will.deacon@arm.com (Will Deacon)
To: linux-arm-kernel@lists.infradead.org
Subject: [PATCH v4 7/8] ARM: mm: allow non-text sections to be non-executable
Date: Tue, 26 Aug 2014 15:43:03 +0100	[thread overview]
Message-ID: <20140826144303.GX23445@arm.com> (raw)
In-Reply-To: <CAGXu5jLnXeavr4E4YF9jtB03iA-y4vLZjf83a8ABzUC-hdkz9w@mail.gmail.com>

On Wed, Aug 20, 2014 at 01:37:14PM +0100, Kees Cook wrote:
> On Tue, Aug 19, 2014 at 7:33 AM, Will Deacon <will.deacon@arm.com> wrote:
> > On Wed, Aug 13, 2014 at 06:06:32PM +0100, Kees Cook wrote:
> >> +/*
> >> + * Updates section permissions only for the current mm (sections are
> >> + * copied into each mm). During startup, this is the init_mm.
> >> + */
> >> +static inline void section_update(unsigned long addr, pmdval_t mask,
> >> +                               pmdval_t prot)
> >> +{
> >> +     struct mm_struct *mm;
> >> +     pmd_t *pmd;
> >> +
> >> +     mm = current->active_mm;
> >> +     pmd = pmd_offset(pud_offset(pgd_offset(mm, addr), addr), addr);
> >> +
> >> +#ifdef CONFIG_ARM_LPAE
> >> +     pmd[0] = __pmd((pmd_val(pmd[0]) & mask) | prot);
> >> +#else
> >> +     if (addr & SECTION_SIZE)
> >> +             pmd[1] = __pmd((pmd_val(pmd[1]) & mask) | prot);
> >> +     else
> >> +             pmd[0] = __pmd((pmd_val(pmd[0]) & mask) | prot);
> >> +#endif
> >> +     flush_pmd_entry(pmd);
> >> +     local_flush_tlb_kernel_range(addr, addr + SECTION_SIZE);
> >
> > Why only a local flush? You're changing global mappings here, right?
> 
> Yes, but with the a15 errata, it cannot use a global flush. As a
> result, section_update can only be used by a single CPU which is how
> the usage is managed. Perhaps I should add some comments to that
> effect? (There was a thread a few months ago on this problem and this
> shook out as a solution.)

Hmm, so do you mandate that preemption is disabled during sections of code
where the permissions must be changed after boot? (e.g. ftrace patching)

Will

  reply	other threads:[~2014-08-26 14:42 UTC|newest]

Thread overview: 52+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2014-08-13 17:06 [PATCH v4 0/8] arm: support CONFIG_RODATA Kees Cook
2014-08-13 17:06 ` Kees Cook
2014-08-13 17:06 ` [PATCH v4 1/8] arm: use generic fixmap.h Kees Cook
2014-08-13 17:06   ` Kees Cook
2014-08-13 17:06 ` [PATCH v4 2/8] ARM: expand fixmap region to 3MB Kees Cook
2014-08-13 17:06   ` Kees Cook
2014-08-19 12:26   ` Will Deacon
2014-08-19 12:26     ` Will Deacon
2014-08-20 12:16     ` Kees Cook
2014-08-20 12:16       ` Kees Cook
2014-08-26 14:37       ` Will Deacon
2014-08-26 14:37         ` Will Deacon
2014-08-13 17:06 ` [PATCH v4 3/8] arm: fixmap: implement __set_fixmap() Kees Cook
2014-08-13 17:06   ` Kees Cook
2014-08-13 17:06 ` [PATCH v4 4/8] arm: use fixmap for text patching when text is RO Kees Cook
2014-08-13 17:06   ` Kees Cook
2014-08-19 12:29   ` Will Deacon
2014-08-19 12:29     ` Will Deacon
2014-08-20 12:28     ` Kees Cook
2014-08-20 12:28       ` Kees Cook
2014-09-03 21:43       ` Kees Cook
2014-09-03 21:43         ` Kees Cook
2014-09-04  9:27         ` Will Deacon
2014-09-04  9:27           ` Will Deacon
2014-09-04 14:00           ` Kees Cook
2014-09-04 14:00             ` Kees Cook
2014-09-04 14:06             ` Will Deacon
2014-09-04 14:06               ` Will Deacon
2014-08-13 17:06 ` [PATCH v4 5/8] ARM: kexec: Make .text R/W in machine_kexec Kees Cook
2014-08-13 17:06   ` Kees Cook
2014-08-13 17:06 ` [PATCH v4 6/8] arm: kgdb: Handle read-only text / modules Kees Cook
2014-08-13 17:06   ` Kees Cook
2014-08-13 17:06 ` [PATCH v4 7/8] ARM: mm: allow non-text sections to be non-executable Kees Cook
2014-08-13 17:06   ` Kees Cook
2014-08-19 12:33   ` Will Deacon
2014-08-19 12:33     ` Will Deacon
2014-08-20 12:37     ` Kees Cook
2014-08-20 12:37       ` Kees Cook
2014-08-26 14:43       ` Will Deacon [this message]
2014-08-26 14:43         ` Will Deacon
2014-08-29 16:04         ` Kees Cook
2014-08-29 16:04           ` Kees Cook
2014-08-31 14:59           ` Rabin Vincent
2014-08-31 14:59             ` Rabin Vincent
2014-08-13 17:06 ` [PATCH v4 8/8] ARM: mm: allow text and rodata sections to be read-only Kees Cook
2014-08-13 17:06   ` Kees Cook
2014-08-19 12:36   ` Will Deacon
2014-08-19 12:36     ` Will Deacon
2014-08-20 12:52     ` Kees Cook
2014-08-20 12:52       ` Kees Cook
2014-08-13 17:38 ` [PATCH v4 0/8] arm: support CONFIG_RODATA Nicolas Pitre
2014-08-13 17:38   ` Nicolas Pitre

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