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From: Dave Hansen <dave.hansen@intel.com>
To: Yu-cheng Yu <yu-cheng.yu@intel.com>,
	x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>,
	linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org,
	linux-mm@kvack.org, linux-arch@vger.kernel.org,
	linux-api@vger.kernel.org, Arnd Bergmann <arnd@arndb.de>,
	Andy Lutomirski <luto@kernel.org>,
	Balbir Singh <bsingharora@gmail.com>,
	Borislav Petkov <bp@alien8.de>,
	Cyrill Gorcunov <gorcunov@gmail.com>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	Eugene Syromiatnikov <esyr@redhat.com>,
	Florian Weimer <fweimer@redhat.com>,
	"H.J. Lu" <hjl.tools@gmail.com>, Jann Horn <jannh@google.com>,
	Jonathan Corbet <corbet@lwn.net>,
	Kees Cook <keescook@chromium.org>,
	Mike Kravetz <mike.kravetz@oracle.com>,
	Nadav Amit <nadav.amit@gmail.com>,
	Oleg Nesterov <oleg@redhat.com>, Pavel Machek <pavel@ucw.cz>,
	Peter Zijlstra <peterz@infradead.org>,
	Randy Dunlap <rdunlap@infradead.org>,
	"Ravi V. Shankar" <ravi.v.shankar@intel.com>,
	Vedvyas Shanbhogue <vedvyas.shanbhogue@intel.com>,
	Dave Martin <Dave.Martin@arm.com>,
	x86-patch-review@intel.com
Subject: Re: [RFC PATCH v9 10/27] x86/mm: Update pte_modify, pmd_modify, and _PAGE_CHG_MASK for _PAGE_DIRTY_SW
Date: Wed, 26 Feb 2020 14:02:06 -0800	[thread overview]
Message-ID: <c215a795-1411-9ab0-10a6-520dd4771016@intel.com> (raw)
In-Reply-To: <20200205181935.3712-11-yu-cheng.yu@intel.com>

The subject really needs work.  Could you think of a way to summarize
the changes here in english as opposed to just listing the symbols you
modified?

I think we could probably just auto-generate subjects for patches if the
existing one were sufficient.

On 2/5/20 10:19 AM, Yu-cheng Yu wrote:
> After the introduction of _PAGE_DIRTY_SW, pte_modify and pmd_modify need to
> set the Dirty bit accordingly: if Shadow Stack is enabled and _PAGE_RW is
> cleared, use _PAGE_DIRTY_SW; otherwise _PAGE_DIRTY_HW.

You've basically gone and written the code's if() statement in english
here.  That doesn't really help me understand the patch.

> Since the Dirty bit is modify by pte_modify(), remove _PAGE_DIRTY_HW from
> PAGE_CHG_MASK.

			 ^ modified

This is a great example of a changelog that adds very little value.
It's following the comments and doing what they say, but it's pretty
obvious that the analysis stopped there.

What *kinds* of bits are in _PAGE_CHG_MASK or not?  What changed about
_PAGE_DIRTY_HW.  By this definition, shouldn't _PAGE_DIRTY_SW have
technically been in this mask before this patch?

> diff --git a/arch/x86/include/asm/pgtable.h b/arch/x86/include/asm/pgtable.h
> index 62aeb118bc36..2733e7ec16b3 100644
> --- a/arch/x86/include/asm/pgtable.h
> +++ b/arch/x86/include/asm/pgtable.h
> @@ -702,6 +702,14 @@ static inline pte_t pte_modify(pte_t pte, pgprot_t newprot)
>  	val &= _PAGE_CHG_MASK;
>  	val |= check_pgprot(newprot) & ~_PAGE_CHG_MASK;
>  	val = flip_protnone_guard(oldval, val, PTE_PFN_MASK);
> +
> +	if (pte_dirty(pte)) {
> +		if (static_cpu_has(X86_FEATURE_SHSTK) && !(val & _PAGE_RW))
> +			val |= _PAGE_DIRTY_SW;
> +		else
> +			val |= _PAGE_DIRTY_HW;
> +	}
> +
>  	return __pte(val);
>  }

OK, so this is a path we use for changing bunches of PTEs to 'newprot'.
 It doesn't use the pte_*() helpers that the previous patch fixed up, so
we need a new site.

Right?

Maybe that would make good changelog text.

Also, couldn't we just have a pte_fixup() function or something that did
this logic and could be shared?

> @@ -712,6 +720,14 @@ static inline pmd_t pmd_modify(pmd_t pmd, pgprot_t newprot)
>  	val &= _HPAGE_CHG_MASK;
>  	val |= check_pgprot(newprot) & ~_HPAGE_CHG_MASK;
>  	val = flip_protnone_guard(oldval, val, PHYSICAL_PMD_PAGE_MASK);
> +
> +	if (pmd_dirty(pmd)) {
> +		if (static_cpu_has(X86_FEATURE_SHSTK) && !(val & _PAGE_RW))
> +			val |= _PAGE_DIRTY_SW;
> +		else
> +			val |= _PAGE_DIRTY_HW;
> +	}
> +
>  	return __pmd(val);
>  }
>  
> diff --git a/arch/x86/include/asm/pgtable_types.h b/arch/x86/include/asm/pgtable_types.h
> index 826823df917f..e7e28bf7e919 100644
> --- a/arch/x86/include/asm/pgtable_types.h
> +++ b/arch/x86/include/asm/pgtable_types.h
> @@ -150,8 +150,8 @@
>   * instance, and is *not* included in this mask since
>   * pte_modify() does modify it.
>   */
> -#define _PAGE_CHG_MASK	(PTE_PFN_MASK | _PAGE_PCD | _PAGE_PWT |		\
> -			 _PAGE_SPECIAL | _PAGE_ACCESSED | _PAGE_DIRTY_HW |	\
> +#define _PAGE_CHG_MASK	(PTE_PFN_MASK | _PAGE_PCD | _PAGE_PWT |	\
> +			 _PAGE_SPECIAL | _PAGE_ACCESSED |	\
>  			 _PAGE_SOFT_DIRTY | _PAGE_DEVMAP)
>  #define _HPAGE_CHG_MASK (_PAGE_CHG_MASK | _PAGE_PSE)




  reply	other threads:[~2020-02-26 22:02 UTC|newest]

Thread overview: 107+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-02-05 18:19 [RFC PATCH v9 00/27] Control-flow Enforcement: Shadow Stack Yu-cheng Yu
2020-02-05 18:19 ` [RFC PATCH v9 01/27] Documentation/x86: Add CET description Yu-cheng Yu
2020-02-06  0:16   ` Randy Dunlap
2020-02-06 20:17     ` Yu-cheng Yu
2020-02-25 20:02   ` Kees Cook
2020-02-28 15:55     ` Yu-cheng Yu
2020-02-26 17:57   ` Dave Hansen
2020-03-09 17:00     ` Yu-cheng Yu
2020-03-09 17:21       ` Dave Hansen
2020-03-09 19:27         ` Yu-cheng Yu
2020-03-09 19:35           ` Dave Hansen
2020-03-09 19:50             ` H.J. Lu
2020-03-09 20:16               ` Andy Lutomirski
2020-03-09 20:54                 ` H.J. Lu
2020-03-09 20:59                   ` Dave Hansen
2020-03-09 21:12                     ` H.J. Lu
2020-03-09 22:02                       ` Andy Lutomirski
2020-03-09 22:19                       ` Dave Hansen
2020-03-09 23:11                         ` H.J. Lu
2020-03-09 23:20                           ` Dave Hansen
2020-03-09 23:51                             ` H.J. Lu
2020-03-09 23:59                               ` Andy Lutomirski
2020-03-10  0:08                                 ` H.J. Lu
2020-03-10  1:21                                   ` Andy Lutomirski
2020-03-10  2:13                                     ` H.J. Lu
2020-02-05 18:19 ` [RFC PATCH v9 02/27] x86/cpufeatures: Add CET CPU feature flags for Control-flow Enforcement Technology (CET) Yu-cheng Yu
2020-02-25 20:02   ` Kees Cook
2020-02-05 18:19 ` [RFC PATCH v9 03/27] x86/fpu/xstate: Introduce CET MSR XSAVES supervisor states Yu-cheng Yu
2020-02-25 20:04   ` Kees Cook
2020-02-05 18:19 ` [RFC PATCH v9 04/27] x86/cet: Add control-protection fault handler Yu-cheng Yu
2020-02-25 20:06   ` Kees Cook
2020-02-26 17:10   ` Dave Hansen
2020-03-05 20:44     ` Yu-cheng Yu
2020-02-05 18:19 ` [RFC PATCH v9 05/27] x86/cet/shstk: Add Kconfig option for user-mode Shadow Stack protection Yu-cheng Yu
2020-02-25 20:07   ` Kees Cook
2020-02-26 17:03   ` Dave Hansen
2020-02-26 19:57     ` Pavel Machek
2020-03-05 20:38     ` Yu-cheng Yu
2020-02-26 18:05   ` Dave Hansen
2020-02-27  1:02     ` H.J. Lu
2020-02-27  1:16       ` Dave Hansen
2020-02-27  2:11         ` H.J. Lu
2020-02-27  3:57           ` Andy Lutomirski
2020-02-27 18:03             ` Dave Hansen
2020-03-06 18:37     ` Yu-cheng Yu
2020-03-06 19:02       ` Dave Hansen
2020-03-06 21:16         ` Yu-cheng Yu
2020-02-05 18:19 ` [RFC PATCH v9 06/27] mm: Introduce VM_SHSTK for Shadow Stack memory Yu-cheng Yu
2020-02-25 20:07   ` Kees Cook
2020-02-26 18:07   ` Dave Hansen
2020-02-05 18:19 ` [RFC PATCH v9 07/27] Add guard pages around a Shadow Stack Yu-cheng Yu
2020-02-25 20:11   ` Kees Cook
2020-02-26 18:17   ` Dave Hansen
2020-02-05 18:19 ` [RFC PATCH v9 08/27] x86/mm: Change _PAGE_DIRTY to _PAGE_DIRTY_HW Yu-cheng Yu
2020-02-25 20:12   ` Kees Cook
2020-02-26 18:20   ` Dave Hansen
2020-02-05 18:19 ` [RFC PATCH v9 09/27] x86/mm: Introduce _PAGE_DIRTY_SW Yu-cheng Yu
2020-02-25 20:12   ` Kees Cook
2020-02-26 21:35   ` Dave Hansen
2020-04-01 19:08     ` Yu-cheng Yu
2020-04-01 19:22       ` Dave Hansen
2020-02-05 18:19 ` [RFC PATCH v9 10/27] x86/mm: Update pte_modify, pmd_modify, and _PAGE_CHG_MASK for _PAGE_DIRTY_SW Yu-cheng Yu
2020-02-26 22:02   ` Dave Hansen [this message]
2020-02-05 18:19 ` [RFC PATCH v9 11/27] drm/i915/gvt: Change _PAGE_DIRTY to _PAGE_DIRTY_BITS Yu-cheng Yu
2020-02-25 20:13   ` Kees Cook
2020-02-26 22:04   ` Dave Hansen
2020-04-03 15:42     ` Yu-cheng Yu
2020-02-05 18:19 ` [RFC PATCH v9 12/27] x86/mm: Modify ptep_set_wrprotect and pmdp_set_wrprotect for _PAGE_DIRTY_SW Yu-cheng Yu
2020-02-25 20:14   ` Kees Cook
2020-02-26 22:20   ` Dave Hansen
2020-02-05 18:19 ` [RFC PATCH v9 13/27] x86/mm: Shadow Stack page fault error checking Yu-cheng Yu
2020-02-25 20:16   ` Kees Cook
2020-02-26 22:47   ` Dave Hansen
2020-02-05 18:19 ` [RFC PATCH v9 14/27] mm: Handle Shadow Stack page fault Yu-cheng Yu
2020-02-25 20:20   ` Kees Cook
2020-03-05 18:30     ` Yu-cheng Yu
2020-02-27  0:08   ` Dave Hansen
2020-04-07 18:14     ` Yu-cheng Yu
2020-04-07 22:21       ` Dave Hansen
2020-04-08 18:18         ` Yu-cheng Yu
2020-02-05 18:19 ` [RFC PATCH v9 15/27] mm: Handle THP/HugeTLB " Yu-cheng Yu
2020-02-25 20:59   ` Kees Cook
2020-03-13 22:00     ` Yu-cheng Yu
2020-02-05 18:19 ` [RFC PATCH v9 16/27] mm: Update can_follow_write_pte() for Shadow Stack Yu-cheng Yu
2020-02-27  0:34   ` Dave Hansen
2020-02-05 18:19 ` [RFC PATCH v9 17/27] x86/cet/shstk: User-mode Shadow Stack support Yu-cheng Yu
2020-02-25 21:07   ` Kees Cook
2020-02-27  0:55   ` Dave Hansen
2020-02-05 18:19 ` [RFC PATCH v9 18/27] x86/cet/shstk: Introduce WRUSS instruction Yu-cheng Yu
2020-02-25 21:10   ` Kees Cook
2020-03-05 18:39     ` Yu-cheng Yu
2020-02-05 18:19 ` [RFC PATCH v9 19/27] x86/cet/shstk: Handle signals for Shadow Stack Yu-cheng Yu
2020-02-25 21:17   ` Kees Cook
2020-02-05 18:19 ` [RFC PATCH v9 20/27] ELF: UAPI and Kconfig additions for ELF program properties Yu-cheng Yu
2020-02-05 18:19 ` [RFC PATCH v9 21/27] binfmt_elf: Define GNU_PROPERTY_X86_FEATURE_1_AND Yu-cheng Yu
2020-02-25 21:18   ` Kees Cook
2020-02-05 18:19 ` [RFC PATCH v9 22/27] ELF: Add ELF program property parsing support Yu-cheng Yu
2020-02-25 21:20   ` Kees Cook
2020-02-05 18:19 ` [RFC PATCH v9 23/27] ELF: Introduce arch_setup_elf_property() Yu-cheng Yu
2020-02-05 18:19 ` [RFC PATCH v9 24/27] x86/cet/shstk: ELF header parsing for Shadow Stack Yu-cheng Yu
2020-02-25 21:22   ` Kees Cook
2020-02-05 18:19 ` [RFC PATCH v9 25/27] x86/cet/shstk: Handle thread " Yu-cheng Yu
2020-02-25 21:29   ` Kees Cook
2020-03-25 21:51     ` Yu-cheng Yu
2020-02-05 18:19 ` [RFC PATCH v9 26/27] mm/mmap: Add Shadow Stack pages to memory accounting Yu-cheng Yu
2020-02-05 18:19 ` [RFC PATCH v9 27/27] x86/cet/shstk: Add arch_prctl functions for Shadow Stack Yu-cheng Yu
2020-02-25 21:31 ` [RFC PATCH v9 00/27] Control-flow Enforcement: " Kees Cook

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