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From: Catalin Marinas <catalin.marinas@arm.com>
To: Dave Martin <Dave.Martin@arm.com>
Cc: Andrey Konovalov <andreyknvl@google.com>,
	linux-arm-kernel@lists.infradead.org, linux-mm@kvack.org,
	linux-kernel@vger.kernel.org, amd-gfx@lists.freedesktop.org,
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	Luc Van Oostenryck <luc.vanoostenryck@gmail.com>
Subject: Re: [PATCH v17 03/15] arm64: Introduce prctl() options to control the tagged user addresses ABI
Date: Thu, 13 Jun 2019 16:35:07 +0100
Message-ID: <20190613153505.GU28951@C02TF0J2HF1T.local> (raw)
In-Reply-To: <20190613111659.GX28398@e103592.cambridge.arm.com>

On Thu, Jun 13, 2019 at 12:16:59PM +0100, Dave P Martin wrote:
> On Wed, Jun 12, 2019 at 01:43:20PM +0200, Andrey Konovalov wrote:
> > From: Catalin Marinas <catalin.marinas@arm.com>
> > 
> > It is not desirable to relax the ABI to allow tagged user addresses into
> > the kernel indiscriminately. This patch introduces a prctl() interface
> > for enabling or disabling the tagged ABI with a global sysctl control
> > for preventing applications from enabling the relaxed ABI (meant for
> > testing user-space prctl() return error checking without reconfiguring
> > the kernel). The ABI properties are inherited by threads of the same
> > application and fork()'ed children but cleared on execve().
> > 
> > The PR_SET_TAGGED_ADDR_CTRL will be expanded in the future to handle
> > MTE-specific settings like imprecise vs precise exceptions.
> > 
> > Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
> > ---
> >  arch/arm64/include/asm/processor.h   |  6 +++
> >  arch/arm64/include/asm/thread_info.h |  1 +
> >  arch/arm64/include/asm/uaccess.h     |  3 +-
> >  arch/arm64/kernel/process.c          | 67 ++++++++++++++++++++++++++++
> >  include/uapi/linux/prctl.h           |  5 +++
> >  kernel/sys.c                         | 16 +++++++
> >  6 files changed, 97 insertions(+), 1 deletion(-)
> > 
> > diff --git a/arch/arm64/include/asm/processor.h b/arch/arm64/include/asm/processor.h
> > index fcd0e691b1ea..fee457456aa8 100644
> > --- a/arch/arm64/include/asm/processor.h
> > +++ b/arch/arm64/include/asm/processor.h
> > @@ -307,6 +307,12 @@ extern void __init minsigstksz_setup(void);
> >  /* PR_PAC_RESET_KEYS prctl */
> >  #define PAC_RESET_KEYS(tsk, arg)	ptrauth_prctl_reset_keys(tsk, arg)
> >  
> > +/* PR_TAGGED_ADDR prctl */
> 
> (A couple of comments I missed in my last reply:)
> 
> Name mismatch?

Yeah, it went through several names but it seems that I didn't update
all places.

> > +long set_tagged_addr_ctrl(unsigned long arg);
> > +long get_tagged_addr_ctrl(void);
> > +#define SET_TAGGED_ADDR_CTRL(arg)	set_tagged_addr_ctrl(arg)
> > +#define GET_TAGGED_ADDR_CTRL()		get_tagged_addr_ctrl()
> > +
> 
> [...]
> 
> > diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c
> > index 3767fb21a5b8..69d0be1fc708 100644
> > --- a/arch/arm64/kernel/process.c
> > +++ b/arch/arm64/kernel/process.c
> > @@ -30,6 +30,7 @@
> >  #include <linux/kernel.h>
> >  #include <linux/mm.h>
> >  #include <linux/stddef.h>
> > +#include <linux/sysctl.h>
> >  #include <linux/unistd.h>
> >  #include <linux/user.h>
> >  #include <linux/delay.h>
> > @@ -323,6 +324,7 @@ void flush_thread(void)
> >  	fpsimd_flush_thread();
> >  	tls_thread_flush();
> >  	flush_ptrace_hw_breakpoint(current);
> > +	clear_thread_flag(TIF_TAGGED_ADDR);
> >  }
> >  
> >  void release_thread(struct task_struct *dead_task)
> > @@ -552,3 +554,68 @@ void arch_setup_new_exec(void)
> >  
> >  	ptrauth_thread_init_user(current);
> >  }
> > +
> > +/*
> > + * Control the relaxed ABI allowing tagged user addresses into the kernel.
> > + */
> > +static unsigned int tagged_addr_prctl_allowed = 1;
> > +
> > +long set_tagged_addr_ctrl(unsigned long arg)
> > +{
> > +	if (!tagged_addr_prctl_allowed)
> > +		return -EINVAL;
> 
> So, tagging can actually be locked on by having a process enable it and
> then some possibly unrelated process clearing tagged_addr_prctl_allowed.
> That feels a bit weird.

The problem is that if you disable the ABI globally, lots of
applications would crash. This sysctl is meant as a way to disable the
opt-in to the TBI ABI. Another option would be a kernel command line
option (I'm not keen on a Kconfig option).

> Do we want to allow a process that has tagging on to be able to turn
> it off at all?  Possibly things like CRIU might want to do that.

I left it in for symmetry but I don't expect it to be used. A potential
use-case is doing it per subsequent threads in an application.

> > +	if (is_compat_task())
> > +		return -EINVAL;
> > +	if (arg & ~PR_TAGGED_ADDR_ENABLE)
> > +		return -EINVAL;
> 
> How do we expect this argument to be extended in the future?

Yes, for MTE. That's why I wouldn't allow random bits here.

> I'm wondering whether this is really a bitmask or an enum, or a mixture
> of the two.  Maybe it doesn't matter.

User may want to set PR_TAGGED_ADDR_ENABLE | PR_MTE_PRECISE in a single
call.

> > +	if (arg & PR_TAGGED_ADDR_ENABLE)
> > +		set_thread_flag(TIF_TAGGED_ADDR);
> > +	else
> > +		clear_thread_flag(TIF_TAGGED_ADDR);
> 
> I think update_thread_flag() could be used here.

Yes. I forgot you added this.

-- 
Catalin

  reply index

Thread overview: 51+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-06-12 11:43 [PATCH v17 00/15] arm64: untag user pointers passed to the kernel Andrey Konovalov
2019-06-12 11:43 ` [PATCH v17 01/15] arm64: untag user pointers in access_ok and __uaccess_mask_ptr Andrey Konovalov
2019-06-12 14:26   ` Vincenzo Frascino
2019-06-12 11:43 ` [PATCH v17 02/15] lib, arm64: untag user pointers in strn*_user Andrey Konovalov
2019-06-12 14:28   ` Vincenzo Frascino
2019-06-12 11:43 ` [PATCH v17 03/15] arm64: Introduce prctl() options to control the tagged user addresses ABI Andrey Konovalov
2019-06-12 14:30   ` Vincenzo Frascino
2019-06-12 14:55   ` Catalin Marinas
2019-06-13 11:02   ` Dave Martin
2019-06-13 15:26     ` Catalin Marinas
2019-06-14  5:13       ` Kees Cook
2019-06-18  9:18         ` Dave Martin
2019-06-13 11:16   ` Dave Martin
2019-06-13 15:35     ` Catalin Marinas [this message]
2019-06-13 15:45       ` Vincenzo Frascino
2019-06-13 15:57         ` Catalin Marinas
2019-06-13 16:15           ` Vincenzo Frascino
2019-06-17 13:56   ` Catalin Marinas
2019-06-17 16:56     ` Szabolcs Nagy
2019-06-17 16:57     ` Evgenii Stepanov
2019-06-17 17:18       ` Catalin Marinas
2019-06-17 21:59         ` Evgenii Stepanov
2019-06-19 14:45   ` Andrey Konovalov
2019-06-19 15:29     ` Catalin Marinas
2019-06-12 11:43 ` [PATCH v17 04/15] mm, arm64: untag user pointers passed to memory syscalls Andrey Konovalov
2019-06-12 14:31   ` Vincenzo Frascino
2019-06-19 15:55   ` Khalid Aziz
2019-06-19 16:46     ` Khalid Aziz
2019-06-24 14:22       ` Andrey Konovalov
2019-06-12 11:43 ` [PATCH v17 05/15] mm, arm64: untag user pointers in mm/gup.c Andrey Konovalov
2019-06-12 14:33   ` Vincenzo Frascino
2019-06-19 16:41   ` Khalid Aziz
2019-06-12 11:43 ` [PATCH v17 06/15] mm, arm64: untag user pointers in get_vaddr_frames Andrey Konovalov
2019-06-12 14:34   ` Vincenzo Frascino
2019-06-19 16:48   ` Khalid Aziz
2019-06-12 11:43 ` [PATCH v17 07/15] fs, arm64: untag user pointers in copy_mount_options Andrey Konovalov
2019-06-12 14:35   ` Vincenzo Frascino
2019-06-19 20:01   ` Khalid Aziz
2019-06-12 11:43 ` [PATCH v17 08/15] userfaultfd, arm64: untag user pointers Andrey Konovalov
2019-06-12 14:40   ` Vincenzo Frascino
2019-06-12 11:43 ` [PATCH v17 09/15] drm/amdgpu, " Andrey Konovalov
2019-06-12 11:43 ` [PATCH v17 10/15] drm/radeon, arm64: untag user pointers in radeon_gem_userptr_ioctl Andrey Konovalov
2019-06-12 11:43 ` [PATCH v17 11/15] IB/mlx4, arm64: untag user pointers in mlx4_get_umem_mr Andrey Konovalov
2019-06-12 11:43 ` [PATCH v17 12/15] media/v4l2-core, arm64: untag user pointers in videobuf_dma_contig_user_get Andrey Konovalov
2019-06-19 20:05   ` Khalid Aziz
2019-06-12 11:43 ` [PATCH v17 13/15] tee/shm, arm64: untag user pointers in tee_shm_register Andrey Konovalov
2019-06-12 11:43 ` [PATCH v17 14/15] vfio/type1, arm64: untag user pointers in vaddr_get_pfn Andrey Konovalov
2019-06-12 14:41   ` Vincenzo Frascino
2019-06-12 15:58   ` Auger Eric
2019-06-12 11:43 ` [PATCH v17 15/15] selftests, arm64: add a selftest for passing tagged pointers to kernel Andrey Konovalov
2019-06-12 12:30   ` Szabolcs Nagy

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