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From: Yu-cheng Yu <yu-cheng.yu@intel.com>
To: Andy Lutomirski <luto@amacapital.net>
Cc: Eugene Syromiatnikov <esyr@redhat.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>,
	Balbir Singh <bsingharora@gmail.com>,
	Cyrill Gorcunov <gorcunov@gmail.com>,
	Dave Hansen <dave.hansen@linux.intel.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
Subject: Re: [RFC PATCH v4 3/9] x86/cet/ibt: Add IBT legacy code bitmap allocation function
Date: Fri, 05 Oct 2018 09:58:24 -0700	[thread overview]
Message-ID: <aa5a061c159471f410d677af6a609793906cece1.camel@intel.com> (raw)
In-Reply-To: <5BF3AE8F-CC2A-4160-9FF6-FEA171A76371@amacapital.net>

On Fri, 2018-10-05 at 09:28 -0700, Andy Lutomirski wrote:
> > On Oct 5, 2018, at 9:13 AM, Yu-cheng Yu <yu-cheng.yu@intel.com> wrote:
> > 
> > > On Wed, 2018-10-03 at 21:57 +0200, Eugene Syromiatnikov wrote:
> > > > On Fri, Sep 21, 2018 at 08:05:47AM -0700, Yu-cheng Yu wrote:
> > > > Indirect branch tracking provides an optional legacy code bitmap
> > > > that indicates locations of non-IBT compatible code.  When set,
> > > > each bit in the bitmap represents a page in the linear address is
> > > > legacy code.
> > > > 
> > > > We allocate the bitmap only when the application requests it.
> > > > Most applications do not need the bitmap.
> > > > 
> > > > Signed-off-by: Yu-cheng Yu <yu-cheng.yu@intel.com>
> > > > ---
> > > > arch/x86/kernel/cet.c | 45 +++++++++++++++++++++++++++++++++++++++++++
> > > > 1 file changed, 45 insertions(+)
> > > > 
> > > > diff --git a/arch/x86/kernel/cet.c b/arch/x86/kernel/cet.c
> > > > index 6adfe795d692..a65d9745af08 100644
> > > > --- a/arch/x86/kernel/cet.c
> > > > +++ b/arch/x86/kernel/cet.c
> > > > @@ -314,3 +314,48 @@ void cet_disable_ibt(void)
> > > >    wrmsrl(MSR_IA32_U_CET, r);
> > > >    current->thread.cet.ibt_enabled = 0;
> > > > }
> > > > +
> > > > +int cet_setup_ibt_bitmap(void)
> > > > +{
> > > > +    u64 r;
> > > > +    unsigned long bitmap;
> > > > +    unsigned long size;
> > > > +
> > > > +    if (!cpu_feature_enabled(X86_FEATURE_IBT))
> > > > +        return -EOPNOTSUPP;
> > > > +
> > > > +    if (!current->thread.cet.ibt_bitmap_addr) {
> > > > +        /*
> > > > +         * Calculate size and put in thread header.
> > > > +         * may_expand_vm() needs this information.
> > > > +         */
> > > > +        size = TASK_SIZE / PAGE_SIZE / BITS_PER_BYTE;
> > > 
> > > TASK_SIZE_MAX is likely needed here, as an application can easily switch
> > > between long an 32-bit protected mode.  And then the case of a CPU that
> > > doesn't support 5LPT.
> > 
> > If we had calculated bitmap size from TASK_SIZE_MAX, all 32-bit apps would
> > have
> > failed the allocation for bitmap size > TASK_SIZE.  Please see values below,
> > which is printed from the current code.
> > 
> > Yu-cheng
> > 
> > 
> > x64:
> > TASK_SIZE_MAX    = 0000 7fff ffff f000
> > TASK_SIZE    = 0000 7fff ffff f000
> > bitmap size    = 0000 0000 ffff ffff
> > 
> > x32:
> > TASK_SIZE_MAX    = 0000 7fff ffff f000
> > TASK_SIZE    = 0000 0000 ffff e000
> > bitmap size    = 0000 0000 0001 ffff
> > 
> 
> I haven’t followed all the details here, but I have a general policy of
> objecting to any new use of TASK_SIZE. If you really really need to depend on
> 32-bitness in new code, please figure out what exactly you mean by “32-bit”
> and use an explicit check.

The explicit check would be:

test_thread_flag(TIF_ADDR32) ? IA32_PAGE_OFFSET : TASK_SIZE_MAX

which is the same as TASK_SIZE.

Or, do we want a new macro?

#define IBT_BITMAP_SIZE (test_thread_flag(TIF_ADDR32) ? \
	(IA32_PAGE_OFFSET / PAGE_SIZE / BITS_PER_BYTE) : \
	(TASK_SIZE_MAX / PAGE_SIZE / BITS_PER_BYTE))

Yu-cheng

WARNING: multiple messages have this Message-ID (diff)
From: Yu-cheng Yu <yu-cheng.yu@intel.com>
To: Andy Lutomirski <luto@amacapital.net>
Cc: Eugene Syromiatnikov <esyr@redhat.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>,
	Balbir Singh <bsingharora@gmail.com>,
	Cyrill Gorcunov <gorcunov@gmail.com>,
	Dave Hansen <dave.hansen@linux.intel.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>
Subject: Re: [RFC PATCH v4 3/9] x86/cet/ibt: Add IBT legacy code bitmap allocation function
Date: Fri, 05 Oct 2018 09:58:24 -0700	[thread overview]
Message-ID: <aa5a061c159471f410d677af6a609793906cece1.camel@intel.com> (raw)
Message-ID: <20181005165824.gesR0pEKbEiSpi0kygOc4s-7YGEWyA73Zn4swBYa-2M@z> (raw)
In-Reply-To: <5BF3AE8F-CC2A-4160-9FF6-FEA171A76371@amacapital.net>

On Fri, 2018-10-05 at 09:28 -0700, Andy Lutomirski wrote:
> > On Oct 5, 2018, at 9:13 AM, Yu-cheng Yu <yu-cheng.yu@intel.com> wrote:
> > 
> > > On Wed, 2018-10-03 at 21:57 +0200, Eugene Syromiatnikov wrote:
> > > > On Fri, Sep 21, 2018 at 08:05:47AM -0700, Yu-cheng Yu wrote:
> > > > Indirect branch tracking provides an optional legacy code bitmap
> > > > that indicates locations of non-IBT compatible code.  When set,
> > > > each bit in the bitmap represents a page in the linear address is
> > > > legacy code.
> > > > 
> > > > We allocate the bitmap only when the application requests it.
> > > > Most applications do not need the bitmap.
> > > > 
> > > > Signed-off-by: Yu-cheng Yu <yu-cheng.yu@intel.com>
> > > > ---
> > > > arch/x86/kernel/cet.c | 45 +++++++++++++++++++++++++++++++++++++++++++
> > > > 1 file changed, 45 insertions(+)
> > > > 
> > > > diff --git a/arch/x86/kernel/cet.c b/arch/x86/kernel/cet.c
> > > > index 6adfe795d692..a65d9745af08 100644
> > > > --- a/arch/x86/kernel/cet.c
> > > > +++ b/arch/x86/kernel/cet.c
> > > > @@ -314,3 +314,48 @@ void cet_disable_ibt(void)
> > > >    wrmsrl(MSR_IA32_U_CET, r);
> > > >    current->thread.cet.ibt_enabled = 0;
> > > > }
> > > > +
> > > > +int cet_setup_ibt_bitmap(void)
> > > > +{
> > > > +    u64 r;
> > > > +    unsigned long bitmap;
> > > > +    unsigned long size;
> > > > +
> > > > +    if (!cpu_feature_enabled(X86_FEATURE_IBT))
> > > > +        return -EOPNOTSUPP;
> > > > +
> > > > +    if (!current->thread.cet.ibt_bitmap_addr) {
> > > > +        /*
> > > > +         * Calculate size and put in thread header.
> > > > +         * may_expand_vm() needs this information.
> > > > +         */
> > > > +        size = TASK_SIZE / PAGE_SIZE / BITS_PER_BYTE;
> > > 
> > > TASK_SIZE_MAX is likely needed here, as an application can easily switch
> > > between long an 32-bit protected mode.  And then the case of a CPU that
> > > doesn't support 5LPT.
> > 
> > If we had calculated bitmap size from TASK_SIZE_MAX, all 32-bit apps would
> > have
> > failed the allocation for bitmap size > TASK_SIZE.  Please see values below,
> > which is printed from the current code.
> > 
> > Yu-cheng
> > 
> > 
> > x64:
> > TASK_SIZE_MAX    = 0000 7fff ffff f000
> > TASK_SIZE    = 0000 7fff ffff f000
> > bitmap size    = 0000 0000 ffff ffff
> > 
> > x32:
> > TASK_SIZE_MAX    = 0000 7fff ffff f000
> > TASK_SIZE    = 0000 0000 ffff e000
> > bitmap size    = 0000 0000 0001 ffff
> > 
> 
> I haven’t followed all the details here, but I have a general policy of
> objecting to any new use of TASK_SIZE. If you really really need to depend on
> 32-bitness in new code, please figure out what exactly you mean by “32-bit”
> and use an explicit check.

The explicit check would be:

test_thread_flag(TIF_ADDR32) ? IA32_PAGE_OFFSET : TASK_SIZE_MAX

which is the same as TASK_SIZE.

Or, do we want a new macro?

#define IBT_BITMAP_SIZE (test_thread_flag(TIF_ADDR32) ? \
	(IA32_PAGE_OFFSET / PAGE_SIZE / BITS_PER_BYTE) : \
	(TASK_SIZE_MAX / PAGE_SIZE / BITS_PER_BYTE))

Yu-cheng

  parent reply	other threads:[~2018-10-05 16:58 UTC|newest]

Thread overview: 52+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-09-21 15:05 [RFC PATCH v4 0/9] Control Flow Enforcement: Branch Tracking, PTRACE Yu-cheng Yu
2018-09-21 15:05 ` Yu-cheng Yu
2018-09-21 15:05 ` [RFC PATCH v4 1/9] x86/cet/ibt: Add Kconfig option for user-mode Indirect Branch Tracking Yu-cheng Yu
2018-09-21 15:05   ` Yu-cheng Yu
2018-09-21 15:05 ` [RFC PATCH v4 2/9] x86/cet/ibt: User-mode indirect branch tracking support Yu-cheng Yu
2018-09-21 15:05   ` Yu-cheng Yu
2018-10-03 18:58   ` Eugene Syromiatnikov
2018-10-03 18:58     ` Eugene Syromiatnikov
2018-09-21 15:05 ` [RFC PATCH v4 3/9] x86/cet/ibt: Add IBT legacy code bitmap allocation function Yu-cheng Yu
2018-09-21 15:05   ` Yu-cheng Yu
2018-10-03 19:57   ` Eugene Syromiatnikov
2018-10-03 19:57     ` Eugene Syromiatnikov
2018-10-05 16:13     ` Yu-cheng Yu
2018-10-05 16:13       ` Yu-cheng Yu
2018-10-05 16:28       ` Andy Lutomirski
2018-10-05 16:28         ` Andy Lutomirski
2018-10-05 16:58         ` Yu-cheng Yu [this message]
2018-10-05 16:58           ` Yu-cheng Yu
2018-10-05 17:07           ` Andy Lutomirski
2018-10-05 17:07             ` Andy Lutomirski
2018-10-05 17:26             ` Eugene Syromiatnikov
2018-10-05 17:26               ` Eugene Syromiatnikov
2018-10-10 15:56               ` Yu-cheng Yu
2018-10-10 15:56                 ` Yu-cheng Yu
2018-10-04 16:11   ` Andy Lutomirski
2018-10-04 16:11     ` Andy Lutomirski
2018-09-21 15:05 ` [RFC PATCH v4 4/9] mm/mmap: Add IBT bitmap size to address space limit check Yu-cheng Yu
2018-09-21 15:05   ` Yu-cheng Yu
2018-10-03 20:21   ` Eugene Syromiatnikov
2018-10-03 20:21     ` Eugene Syromiatnikov
2018-09-21 15:05 ` [RFC PATCH v4 5/9] x86/cet/ibt: ELF header parsing for IBT Yu-cheng Yu
2018-09-21 15:05   ` Yu-cheng Yu
2018-09-21 15:05 ` [RFC PATCH v4 6/9] x86/cet/ibt: Add arch_prctl functions " Yu-cheng Yu
2018-09-21 15:05   ` Yu-cheng Yu
2018-10-04 13:28   ` Eugene Syromiatnikov
2018-10-04 13:28     ` Eugene Syromiatnikov
2018-10-04 15:37     ` Yu-cheng Yu
2018-10-04 15:37       ` Yu-cheng Yu
2018-10-04 16:07       ` Florian Weimer
2018-10-04 16:07         ` Florian Weimer
2018-10-04 16:12         ` Andy Lutomirski
2018-10-04 16:12           ` Andy Lutomirski
2018-10-04 16:25           ` Yu-cheng Yu
2018-10-04 16:25             ` Yu-cheng Yu
2018-10-04 16:08       ` Andy Lutomirski
2018-10-04 16:08         ` Andy Lutomirski
2018-09-21 15:05 ` [RFC PATCH v4 7/9] x86/cet/ibt: Add ENDBR to op-code-map Yu-cheng Yu
2018-09-21 15:05   ` Yu-cheng Yu
2018-09-21 15:05 ` [RFC PATCH v4 8/9] x86: Insert endbr32/endbr64 to vDSO Yu-cheng Yu
2018-09-21 15:05   ` Yu-cheng Yu
2018-09-21 15:05 ` [RFC PATCH v4 9/9] x86/cet: Add PTRACE interface for CET Yu-cheng Yu
2018-09-21 15:05   ` Yu-cheng Yu

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