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Date: Sat, 8 Sep 2018 00:33:55 +0530
From: Bhupesh Sharma <bhsharma@...hat.com>
To: Sai Praneeth Prakhya <sai.praneeth.prakhya@...el.com>
Cc: linux-efi@...r.kernel.org,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
x86@...nel.org, "Neri, Ricardo" <ricardo.neri@...el.com>,
Matt Fleming <matt@...eblueprint.co.uk>,
Al Stone <astone@...hat.com>, Borislav Petkov <bp@...en8.de>,
Ingo Molnar <mingo@...nel.org>,
Andy Lutomirski <luto@...nel.org>,
Thomas Gleixner <tglx@...utronix.de>,
Peter Zijlstra <peterz@...radead.org>,
Ard Biesheuvel <ard.biesheuvel@...aro.org>
Subject: Re: [PATCH V4 0/3] Add efi page fault handler to recover from page
On Fri, Sep 7, 2018 at 4:57 AM, Sai Praneeth Prakhya
<sai.praneeth.prakhya@...el.com> wrote:
> From: Sai Praneeth <sai.praneeth.prakhya@...el.com>
>
> There may exist some buggy UEFI firmware implementations that access efi
> memory regions other than EFI_RUNTIME_SERVICES_<CODE/DATA> even after
> the kernel has assumed control of the platform. This violates UEFI
> specification. Hence, provide a debug config option which when enabled
> recovers from page faults caused by buggy firmware.
>
> Page faults triggered by firmware happen at ring 0 and if unhandled,
> hangs the kernel. So, provide an efi specific page fault handler to:
> 1. Avoid panics/hangs caused by buggy firmware.
> 2. Shout loud that the firmware is buggy and hence is not a kernel bug.
>
> The efi page fault handler will check if the access is by
> efi_reset_system().
> 1. If so, then the efi page fault handler will reboot the machine
> through BIOS and not through efi_reset_system().
> 2. If not, then the efi page fault handler will freeze efi_rts_wq and
> schedules a new process.
>
> This issue was reported by Al Stone when he saw that reboot via EFI hangs
> the machine. Upon debugging, I found that it's efi_reset_system() that's
> touching memory regions which it shouldn't. To reproduce the same
> behavior, I have hacked OVMF and made efi_reset_system() buggy. Along
> with efi_reset_system(), I have also modified get_next_high_mono_count()
> and set_virtual_address_map(). They illegally access both boot time and
> other efi regions.
>
> Testing the patch set:
> ----------------------
> 1. Download buggy firmware from here [1].
> 2. Run a qemu instance with this buggy BIOS and boot mainline kernel.
> Add reboot=efi to the kernel command line arguments and after the kernel
> is up and running, type "reboot". The kernel should hang while rebooting.
> 3. With the same setup, boot kernel after applying patches and the
> reboot should work fine. Also please notice warning/error messages
> printed by kernel.
>
> Changes from RFC to V1:
> -----------------------
> 1. Drop "long jump" technique of dealing with illegal access and instead
> use scheduling away from efi_rts_wq.
>
> Changes from V1 to V2:
> ----------------------
> 1. Shortened config name to CONFIG_EFI_WARN_ON_ILLEGAL_ACCESS from
> CONFIG_EFI_WARN_ON_ILLEGAL_ACCESSES.
> 2. Made the config option available only to expert users.
> 3. efi_free_boot_services() should be called only when
> CONFIG_EFI_WARN_ON_ILLEGAL_ACCESS is not enabled. Previously, this
> was part of init/main.c file. As it is an architecture agnostic code,
> moved the change to arch/x86/platform/efi/quirks.c file.
>
> Changes from V2 to V3:
> ----------------------
> 1. Drop treating illegal access to EFI_BOOT_SERVICES_<CODE/DATA> regions
> separatley from illegal accesses to other regions like
> EFI_CONVENTIONAL_MEMORY or EFI_LOADER_<CODE/DATA>.
> In previous versions, illegal access to EFI_BOOT_SERVICES_<CODE/DATA>
> regions were handled by mapping requested region to efi_pgd but from
> V3 they are handled similar to illegal access to other regions i.e by
> freezing efi_rts_wq and scheduling new process.
> 2. Change __efi_init_fixup attribute to __efi_init.
>
> Changes from V3 to V4:
> ----------------------
> 1. Drop saving original memory map passed by kernel. It also means less
> checks in efi page fault handler.
> 2. Change the config name to EFI_PAGE_FAULT_HANDLER to reflect it's
> functionality more appropriatley.
>
> Note:
> -----
> Patch set based on "next" branch in efi tree.
>
> [1] https://drive.google.com/drive/folders/1VozKTms92ifyVHAT0ZDQe55ZYL1UE5wt
>
> Sai Praneeth (3):
> efi: Make efi_rts_work accessible to efi page fault handler
> x86/efi: Add efi page fault handler to recover from page faults caused
> by the firmware
> x86/efi: Introduce EFI_PAGE_FAULT_HANDLER
>
> arch/x86/Kconfig | 18 +++++++++
> arch/x86/include/asm/efi.h | 9 +++++
> arch/x86/mm/fault.c | 9 +++++
> arch/x86/platform/efi/quirks.c | 70 +++++++++++++++++++++++++++++++++
> drivers/firmware/efi/runtime-wrappers.c | 60 ++++++++--------------------
> include/linux/efi.h | 37 +++++++++++++++++
> 6 files changed, 159 insertions(+), 44 deletions(-)
>
> Suggested-by: Matt Fleming <matt@...eblueprint.co.uk>
> Based-on-code-from: Ricardo Neri <ricardo.neri@...el.com>
> Signed-off-by: Sai Praneeth Prakhya <sai.praneeth.prakhya@...el.com>
> Cc: Al Stone <astone@...hat.com>
> Cc: Borislav Petkov <bp@...en8.de>
> Cc: Ingo Molnar <mingo@...nel.org>
> Cc: Andy Lutomirski <luto@...nel.org>
> Cc: Bhupesh Sharma <bhsharma@...hat.com>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Ard Biesheuvel <ard.biesheuvel@...aro.org>
>
> --
> 2.7.4
>
Thanks Sai for this work. I think this a step in the right direction.
I tested this on qemu x86_64 with OVMF firmware modified to access
some random address in the EFI_Reserved_Region. I was able to reboot
the qemu instance successfully with the patches (see logs below) while
without the patchset, reboot earlier used to get stuck.
So, feel free to add:
Tested-by: Bhupesh Sharma <bhsharma@...hat.com>
Qemu Console Logs:
---------------------------
# reboot
<snip..>
[ 11.400004] ------------[ cut here ]------------
[ 11.400137] [Firmware Bug]: Page fault caused by firmware at PA: 0x7e924100
[ 11.400484] WARNING: CPU: 0 PID: 1111 at
arch/x86/platform/efi/quirks.c:691
efi_recover_from_page_fault+0x3b/0xf0
[ 11.400751] Modules linked in:
[ 11.400992] CPU: 0 PID: 1111 Comm: init Not tainted 4.18.0-rc5+ #1
[ 11.401146] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996),
BIOS 0.0.0 02/06/2015
[ 11.401397] RIP: 0010:efi_recover_from_page_fault+0x3b/0xf0
[ 11.401547] Code: e0 03 00 00 e0 6e 8d 91 0f 85 9e 00 00 00 48 81
ff ff 0f 00 00 0f 86 91 00 00 00 48 89 fe 48 c7 c7 b8 e6 5d 91 e8 65
41 00 00 <0f> 0b 83 3d dc 19 8a 01 09 0f 84 89 00 00 00 48 c7 04 24 02
00 00
[ 11.402185] RSP: 0018:ffffb91080d6ba70 EFLAGS: 00000086
[ 11.402330] RAX: 0000000000000000 RBX: ffff98b53e34c980 RCX: ffffffff91845d38
[ 11.402502] RDX: 0000000000000001 RSI: 0000000000000086 RDI: ffffffff91e8986c
[ 11.402706] RBP: ffffb91080d6bb58 R08: 7269662079622064 R09: 00000000000001fe
[ 11.402881] R10: 0000000000000000 R11: 3030313432396537 R12: ffff98b53e34c980
[ 11.403051] R13: 0000000000000002 R14: 000000000000000b R15: 0000000000000001
[ 11.403259] FS: 00007f7d510fe700(0000) GS:ffff98b53f600000(0000)
knlGS:0000000000000000
[ 11.403452] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 11.403602] CR2: 000000007e924100 CR3: 000000007ec9c000 CR4: 00000000000006f0
[ 11.403823] Call Trace:
[ 11.404368] no_context+0x130/0x3a0
[ 11.404509] __do_page_fault+0x39a/0x4b0
[ 11.404623] page_fault+0x1e/0x30
[ 11.404811] RIP: 0010:0xfffffffeffbba977
[ 11.404908] Code: 89 d5 56 53 4d 89 c4 89 cb 48 83 ec 48 e8 cb 05
00 00 84 c0 41 88 c6 74 11 48 8d 15 3e 15 00 00 b9 00 00 00 80 e8 f8
07 00 00 <48> c7 04 25 00 41 92 7e 0a 00 00 00 48 83 3d c5 29 00 00 00
75 30
[ 11.405544] RSP: 0018:ffffb91080d6bc00 EFLAGS: 00000082
[ 11.405683] RAX: 0000000000000041 RBX: 0000000000000000 RCX: ffffb91080d6bae0
[ 11.405849] RDX: 00000000000003f8 RSI: 0000000000000000 RDI: fffffffeffbba93f
[ 11.406016] RBP: 0000000000000000 R08: 0000000000000041 R09: 0000000000000041
[ 11.406184] R10: 00000000000003fd R11: 00000000000003f8 R12: 0000000000000000
[ 11.406369] R13: 0000000000000000 R14: 0000000000000001 R15: 0000000000000000
[ 11.406593] ? serial8250_console_putchar+0x11/0x20
[ 11.406725] ? efi_call+0x58/0x90
[ 11.406815] ? msg_print_text+0x9c/0x100
[ 11.406927] ? virt_efi_reset_system+0x81/0x100
[ 11.407042] ? efi_reboot+0x85/0xe0
[ 11.407131] ? native_machine_emergency_restart+0x17f/0x260
[ 11.407267] ? clear_local_APIC.part.13+0x1e3/0x220
[ 11.407394] ? __do_sys_reboot+0x1ee/0x210
[ 11.407501] ? __switch_to_asm+0x40/0x70
[ 11.407613] ? __switch_to_asm+0x34/0x70
[ 11.407716] ? __switch_to_asm+0x40/0x70
[ 11.407817] ? __switch_to_asm+0x34/0x70
[ 11.407916] ? __switch_to_asm+0x40/0x70
[ 11.408017] ? __switch_to_asm+0x34/0x70
[ 11.408117] ? __switch_to_asm+0x40/0x70
[ 11.408217] ? __switch_to_asm+0x34/0x70
[ 11.408317] ? __switch_to_asm+0x40/0x70
[ 11.408417] ? __switch_to_asm+0x34/0x70
[ 11.408515] ? __switch_to_asm+0x40/0x70
[ 11.408620] ? __switch_to_asm+0x34/0x70
[ 11.408718] ? __switch_to_asm+0x40/0x70
[ 11.408814] ? __switch_to_asm+0x34/0x70
[ 11.408909] ? __switch_to_asm+0x40/0x70
[ 11.409005] ? __switch_to_asm+0x34/0x70
[ 11.409113] ? __switch_to_asm+0x40/0x70
[ 11.409209] ? __switch_to_asm+0x34/0x70
[ 11.409303] ? __switch_to_asm+0x40/0x70
[ 11.409396] ? __switch_to_asm+0x34/0x70
[ 11.409491] ? __switch_to_asm+0x40/0x70
[ 11.409589] ? __switch_to_asm+0x34/0x70
[ 11.409685] ? __switch_to_asm+0x40/0x70
[ 11.409781] ? __switch_to_asm+0x34/0x70
[ 11.409879] ? __switch_to_asm+0x40/0x70
[ 11.409980] ? __switch_to_asm+0x34/0x70
[ 11.410079] ? __switch_to_asm+0x40/0x70
[ 11.410178] ? __switch_to_asm+0x34/0x70
[ 11.410281] ? do_syscall_64+0x39/0xe0
[ 11.410378] ? entry_SYSCALL_64_after_hwframe+0x44/0xa9
[ 11.410554] ---[ end trace ad3d0a220a88a45b ]---
[ 11.410742] efi: efi_reset_system() buggy! Reboot through BIOS
<snip..>
Thanks,
Bhupesh
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