From: Mark Rutland <mark.rutland-5wv7dgnIgG8@public.gmane.org>
To: Ard Biesheuvel
<ard.biesheuvel-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org>,
James Morse <james.morse-5wv7dgnIgG8@public.gmane.org>
Cc: "linux-efi-u79uwXL29TY76Z2rM5mHXA@public.gmane.org"
<linux-efi-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>,
kernel-hardening-ZwoEplunGu1jrUoiu81ncdBPR1lH4CV8@public.gmane.org,
Matt Fleming
<matt-mF/unelCI9GS6iBeEJttW/XRex20P6io@public.gmane.org>,
Leif Lindholm
<leif.lindholm-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org>,
Borislav Petkov <bp-Gina5bIWoIWzQB+pC5nmwQ@public.gmane.org>,
Roy Franz <rfranz-YGCgFSpz5w/QT0dZR+AlfA@public.gmane.org>,
Ingo Molnar <mingo-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>,
"linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org"
<linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org>
Subject: Re: [PATCH 4/4] ef/libstub: arm/arm64: randomize the base of the UEFI rt services region
Date: Mon, 10 Apr 2017 10:41:42 +0100 [thread overview]
Message-ID: <20170410094124.GA9450@leverpostej> (raw)
In-Reply-To: <CAKv+Gu9CpCWHT=3KboPTtuZVDundtGheKawS=iV_P756RFbaDg-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
On Fri, Apr 07, 2017 at 04:51:16PM +0100, Ard Biesheuvel wrote:
> On 7 April 2017 at 16:47, James Morse <james.morse-5wv7dgnIgG8@public.gmane.org> wrote:
> > On 24/03/17 13:24, Ard Biesheuvel wrote:
> >> Update the allocation logic for the virtual mapping of the UEFI runtime
> >> services to start from a randomized base address if KASLR is in effect,
> >> and if the UEFI firmware exposes an implementation of EFI_RNG_PROTOCOL.
> >>
> >> This makes it more difficult to predict the location of exploitable
> >> data structures in the runtime UEFI firmware, which increases robustness
> >> against attacks. Note that these regions are only mapped during the
> >> time a runtime service call is in progress, and only on a single CPU
> >> at a time, bit give the lack of a downside, let's enable it nonetheless.
> >
> > With next-20170407 on Seattle Overdrive, I get an SError[0] on boot:
> > * Revert "ef/libstub/arm/arm64: Randomize the base of the UEFI rt services region"
> >
> > At which point the machine start booting to a prompt again, (its noisier than
> > usual but looks like double-printing).
> That is quite interesting, to be honest, because that patch should
> effectively be a NOP on systems that do not implement
> EFI_RNG_PROTOCOL.
FWIW, I'm also seeing a crash as a result of this patch, on a Juno R1
with an EFI_RNG_PROTOCOL implementation, with next-20170410 defconfig.
I'm using the Linaro 15.08 toolchain.
----
EFI stub: Booting Linux Kernel...
EFI stub: Using DTB from configuration table
WARNING: this system is using an unsafe pseudo-random implementation of
RngLib!
Synchronous Exception at 0x00000000F80FC7E8
----
If I replace the !nokaslr() in efi_entry() with false, my kernel boots.
If I replace !nokaslr() with true, it fails to boot, even with the call
to efi_get_random_bytes() replaced with status = EFI_ERROR.
The problem appears to be the use of TASK_SIZE, since on arm64 that's:
#define TASK_SIZE (test_thread_flag(TIF_32BIT) ? \
TASK_SIZE_32 : TASK_SIZE_64)
... which would mean that the stub would be trying to dereference whatever it
found in sp_el0. Looking at objdump:
0000000000000160 <efi_entry>:
...
4b4: 94000000 bl 0 <nokaslr>
4b8: 35000280 cbnz w0, 508 <efi_entry+0x3a8>
4bc: d5384100 mrs x0, sp_el0
4c0: f9400004 ldr x4, [x0]
...
So I think we should revert this for now.
Thanks,
Mark.
WARNING: multiple messages have this Message-ID (diff)
From: mark.rutland@arm.com (Mark Rutland)
To: linux-arm-kernel@lists.infradead.org
Subject: [PATCH 4/4] ef/libstub: arm/arm64: randomize the base of the UEFI rt services region
Date: Mon, 10 Apr 2017 10:41:42 +0100 [thread overview]
Message-ID: <20170410094124.GA9450@leverpostej> (raw)
In-Reply-To: <CAKv+Gu9CpCWHT=3KboPTtuZVDundtGheKawS=iV_P756RFbaDg@mail.gmail.com>
On Fri, Apr 07, 2017 at 04:51:16PM +0100, Ard Biesheuvel wrote:
> On 7 April 2017 at 16:47, James Morse <james.morse@arm.com> wrote:
> > On 24/03/17 13:24, Ard Biesheuvel wrote:
> >> Update the allocation logic for the virtual mapping of the UEFI runtime
> >> services to start from a randomized base address if KASLR is in effect,
> >> and if the UEFI firmware exposes an implementation of EFI_RNG_PROTOCOL.
> >>
> >> This makes it more difficult to predict the location of exploitable
> >> data structures in the runtime UEFI firmware, which increases robustness
> >> against attacks. Note that these regions are only mapped during the
> >> time a runtime service call is in progress, and only on a single CPU
> >> at a time, bit give the lack of a downside, let's enable it nonetheless.
> >
> > With next-20170407 on Seattle Overdrive, I get an SError[0] on boot:
> > * Revert "ef/libstub/arm/arm64: Randomize the base of the UEFI rt services region"
> >
> > At which point the machine start booting to a prompt again, (its noisier than
> > usual but looks like double-printing).
> That is quite interesting, to be honest, because that patch should
> effectively be a NOP on systems that do not implement
> EFI_RNG_PROTOCOL.
FWIW, I'm also seeing a crash as a result of this patch, on a Juno R1
with an EFI_RNG_PROTOCOL implementation, with next-20170410 defconfig.
I'm using the Linaro 15.08 toolchain.
----
EFI stub: Booting Linux Kernel...
EFI stub: Using DTB from configuration table
WARNING: this system is using an unsafe pseudo-random implementation of
RngLib!
Synchronous Exception at 0x00000000F80FC7E8
----
If I replace the !nokaslr() in efi_entry() with false, my kernel boots.
If I replace !nokaslr() with true, it fails to boot, even with the call
to efi_get_random_bytes() replaced with status = EFI_ERROR.
The problem appears to be the use of TASK_SIZE, since on arm64 that's:
#define TASK_SIZE (test_thread_flag(TIF_32BIT) ? \
TASK_SIZE_32 : TASK_SIZE_64)
... which would mean that the stub would be trying to dereference whatever it
found in sp_el0. Looking at objdump:
0000000000000160 <efi_entry>:
...
4b4: 94000000 bl 0 <nokaslr>
4b8: 35000280 cbnz w0, 508 <efi_entry+0x3a8>
4bc: d5384100 mrs x0, sp_el0
4c0: f9400004 ldr x4, [x0]
...
So I think we should revert this for now.
Thanks,
Mark.
WARNING: multiple messages have this Message-ID (diff)
From: Mark Rutland <mark.rutland@arm.com>
To: Ard Biesheuvel <ard.biesheuvel@linaro.org>,
James Morse <james.morse@arm.com>
Cc: "linux-efi@vger.kernel.org" <linux-efi@vger.kernel.org>,
kernel-hardening@lists.openwall.com,
Matt Fleming <matt@codeblueprint.co.uk>,
Leif Lindholm <leif.lindholm@linaro.org>,
Borislav Petkov <bp@alien8.de>, Roy Franz <rfranz@cavium.com>,
Ingo Molnar <mingo@kernel.org>,
"linux-arm-kernel@lists.infradead.org"
<linux-arm-kernel@lists.infradead.org>
Subject: [kernel-hardening] Re: [PATCH 4/4] ef/libstub: arm/arm64: randomize the base of the UEFI rt services region
Date: Mon, 10 Apr 2017 10:41:42 +0100 [thread overview]
Message-ID: <20170410094124.GA9450@leverpostej> (raw)
In-Reply-To: <CAKv+Gu9CpCWHT=3KboPTtuZVDundtGheKawS=iV_P756RFbaDg@mail.gmail.com>
On Fri, Apr 07, 2017 at 04:51:16PM +0100, Ard Biesheuvel wrote:
> On 7 April 2017 at 16:47, James Morse <james.morse@arm.com> wrote:
> > On 24/03/17 13:24, Ard Biesheuvel wrote:
> >> Update the allocation logic for the virtual mapping of the UEFI runtime
> >> services to start from a randomized base address if KASLR is in effect,
> >> and if the UEFI firmware exposes an implementation of EFI_RNG_PROTOCOL.
> >>
> >> This makes it more difficult to predict the location of exploitable
> >> data structures in the runtime UEFI firmware, which increases robustness
> >> against attacks. Note that these regions are only mapped during the
> >> time a runtime service call is in progress, and only on a single CPU
> >> at a time, bit give the lack of a downside, let's enable it nonetheless.
> >
> > With next-20170407 on Seattle Overdrive, I get an SError[0] on boot:
> > * Revert "ef/libstub/arm/arm64: Randomize the base of the UEFI rt services region"
> >
> > At which point the machine start booting to a prompt again, (its noisier than
> > usual but looks like double-printing).
> That is quite interesting, to be honest, because that patch should
> effectively be a NOP on systems that do not implement
> EFI_RNG_PROTOCOL.
FWIW, I'm also seeing a crash as a result of this patch, on a Juno R1
with an EFI_RNG_PROTOCOL implementation, with next-20170410 defconfig.
I'm using the Linaro 15.08 toolchain.
----
EFI stub: Booting Linux Kernel...
EFI stub: Using DTB from configuration table
WARNING: this system is using an unsafe pseudo-random implementation of
RngLib!
Synchronous Exception at 0x00000000F80FC7E8
----
If I replace the !nokaslr() in efi_entry() with false, my kernel boots.
If I replace !nokaslr() with true, it fails to boot, even with the call
to efi_get_random_bytes() replaced with status = EFI_ERROR.
The problem appears to be the use of TASK_SIZE, since on arm64 that's:
#define TASK_SIZE (test_thread_flag(TIF_32BIT) ? \
TASK_SIZE_32 : TASK_SIZE_64)
... which would mean that the stub would be trying to dereference whatever it
found in sp_el0. Looking at objdump:
0000000000000160 <efi_entry>:
...
4b4: 94000000 bl 0 <nokaslr>
4b8: 35000280 cbnz w0, 508 <efi_entry+0x3a8>
4bc: d5384100 mrs x0, sp_el0
4c0: f9400004 ldr x4, [x0]
...
So I think we should revert this for now.
Thanks,
Mark.
next prev parent reply other threads:[~2017-04-10 9:41 UTC|newest]
Thread overview: 33+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-03-24 13:24 [PATCH 0/4] efi: libstub enhancements for cmdline parsing and kaslr Ard Biesheuvel
2017-03-24 13:24 ` [kernel-hardening] " Ard Biesheuvel
2017-03-24 13:24 ` Ard Biesheuvel
2017-03-24 13:24 ` [PATCH 2/4] efi/libstub: unify command line param parsing Ard Biesheuvel
2017-03-24 13:24 ` [kernel-hardening] " Ard Biesheuvel
2017-03-24 13:24 ` Ard Biesheuvel
[not found] ` <20170324132410.16628-1-ard.biesheuvel-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org>
2017-03-24 13:24 ` [PATCH 1/4] efi/libstub: fix harmless command line parsing bug Ard Biesheuvel
2017-03-24 13:24 ` [kernel-hardening] " Ard Biesheuvel
2017-03-24 13:24 ` Ard Biesheuvel
2017-03-24 13:24 ` [PATCH 3/4] efi/libstub: arm/arm64: disable debug prints on 'quiet' cmdline arg Ard Biesheuvel
2017-03-24 13:24 ` [kernel-hardening] " Ard Biesheuvel
2017-03-24 13:24 ` Ard Biesheuvel
2017-03-24 14:15 ` Mark Rutland
2017-03-24 14:15 ` [kernel-hardening] " Mark Rutland
2017-03-24 14:15 ` Mark Rutland
2017-03-24 13:24 ` [PATCH 4/4] ef/libstub: arm/arm64: randomize the base of the UEFI rt services region Ard Biesheuvel
2017-03-24 13:24 ` [kernel-hardening] " Ard Biesheuvel
2017-03-24 13:24 ` Ard Biesheuvel
[not found] ` <20170324132410.16628-5-ard.biesheuvel-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org>
2017-04-07 15:47 ` James Morse
2017-04-07 15:47 ` [kernel-hardening] " James Morse
2017-04-07 15:47 ` James Morse
[not found] ` <58E7B478.6010305-5wv7dgnIgG8@public.gmane.org>
2017-04-07 15:51 ` Ard Biesheuvel
2017-04-07 15:51 ` [kernel-hardening] " Ard Biesheuvel
2017-04-07 15:51 ` Ard Biesheuvel
2017-04-07 16:11 ` James Morse
2017-04-07 16:11 ` [kernel-hardening] " James Morse
2017-04-07 16:11 ` James Morse
[not found] ` <CAKv+Gu9CpCWHT=3KboPTtuZVDundtGheKawS=iV_P756RFbaDg-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2017-04-10 9:41 ` Mark Rutland [this message]
2017-04-10 9:41 ` [kernel-hardening] " Mark Rutland
2017-04-10 9:41 ` Mark Rutland
2017-04-10 9:44 ` Ard Biesheuvel
2017-04-10 9:44 ` [kernel-hardening] " Ard Biesheuvel
2017-04-10 9:44 ` Ard Biesheuvel
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