Re: [PATCH for-next v2 0/2] xen/arm: Mitigate straight-line speculation

[Julien Grall <julien@xxxxxxx>]

On 15/03/2021 13:32, Bertrand Marquis wrote:
> Hi Julien,
Hi Bertrand,

> > On 13 Mar 2021, at 16:06, Julien Grall <julien@xxxxxxx> wrote:
> >
> > From: Julien Grall <jgrall@xxxxxxxxxx>
> >
> > Hi all,
> >
> > Last year, Arm released a whitepaper about a new category of speculation.
> > (see [1] and [2]). In short, a processor may be able to speculate past
> > some of the unconditional control flow instructions (e.g eret, smc, br).
> >
> > In some of the cases, the registers will contain values controlled by
> > the guest. While there is no known gadget afterwards, we still want to
> > prevent any leakage in the future.
> >
> > The mitigation is planned in two parts:
> >    1) Arm provided patches for both GCC and LLVM to add speculation barrier
> >    and remove problematic code sequence.
> >    2) Inspection of assembly code and call to higher level (e.g smc in our 
> > case).
> >
> > I still haven't looked at 1) and how to mitigate properly Arm32 (see
> > patch #1) and SMC call. So this issue is not fully addressed.
> >
> > Note that the ERET instruction was already addressed as part of XSA-312.
> On my tests, this serie is breaking the arm64 build:
> | aarch64-poky-linux-ld 
> --sysroot=/home/bermar01/Development/xen-dev/build/profile-fvp-base.prj/tmp/work/fvp_base-poky-linux/xen/4.15+git1-r0/recipe-sysroot
>          -EL  --fix-cortex-a53-843419 --fix-cortex-a53-843419 -r -o built_in.o 
> memcpy.o memcmp.o memmove.o memset.o memchr.o clear_page.o bitops.o 
> find_next_bit.o strchr.o strcmp.o strlen.o strncmp.o strnlen.o strrchr.o
I can't see any build failure with the following GCC:

42sh> aarch64-linux-gnu-gcc
aarch64-linux-gnu-gcc (Ubuntu/Linaro 7.5.0-3ubuntu1~18.04) 7.5.0
Copyright (C) 2017 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

AFAICT, there is also no compilation issue reported by gitlab:

https://gitlab.com/xen-project/patchew/xen/-/pipelines/269989894

What's the version of your compiler? Do you have steps to reproduce your 
setup?
> | arm64/head.S: Assembler messages:
> | arm64/head.S:305: Error: unknown mnemonic `rodata_str' -- `rodata_str(98, "- Boot 
> CPU booting -\r\n")'
This is strange, the code should use RODATA_STR() but here it is in 
lower case. Can you check in your tree whether there some instance of 
the lower case version?
If not, this may just be GAS printing in lower cases.

> | arm64/head.S:331: Error: unknown mnemonic `rodata_str' -- `rodata_str(98, "- Ready 
> -\r\n")'
> | arm64/head.S:365: Error: unknown mnemonic `rodata_str' -- `rodata_str(98, "- CPU 
> ")'
> | make[6]: Leaving directory 
> '/home/bermar01/Development/xen-dev/build/profile-fvp-base.prj/tmp/work/fvp_base-poky-linux/xen/4.15+git1-r0/local-xen/xen/xen/arch/arm/arm64/lib'
> | arm64/head.S:367: Error: unknown mnemonic `rodata_str' -- `rodata_str(98, " 
> booting -\r\n")'
> | arm64/head.S:398: Error: unknown mnemonic `rodata_str' -- `rodata_str(98, "- Ready 
> -\r\n")'
> | arm64/head.S:412: Error: unknown mnemonic `rodata_str' -- `rodata_str(98, "- 
> Current EL ")'
> | arm64/head.S:415: Error: unknown mnemonic `rodata_str' -- `rodata_str(98, " 
> -\r\n")'
> | arm64/head.S:424: Error: unknown mnemonic `rodata_str' -- `rodata_str(98, "- Xen 
> must be entered in NS EL2 mode -\r\n")'
> | arm64/head.S:425: Error: unknown mnemonic `rodata_str' -- `rodata_str(98, "- 
> Please update the bootloader -\r\n")'
> | arm64/head.S:441: Error: unknown mnemonic `rodata_str' -- `rodata_str(98, "- Zero 
> BSS -\r\n")'
> | arm64/head.S:459: Error: unknown mnemonic `rodata_str' -- `rodata_str(98, "- 
> Initialize CPU -\r\n")'
> | arm64/head.S:654: Error: unknown mnemonic `rodata_str' -- `rodata_str(98, "- 
> Unable to build boot page tables - virt and phys addresses clash. -\r\n")'
> | arm64/head.S:666: Error: unknown mnemonic `rodata_str' -- `rodata_str(98, "- 
> Turning on paging -\r\n")'
> | arm64/head.S:800: Error: unknown mnemonic `rodata_str' -- `rodata_str(98, "- Boot 
> failed -\r\n")'
> | arm64/head.S:848: Error: unknown mnemonic `rodata_str' -- `rodata_str(98, "- UART 
> enabled -\r\n")'
> | {standard input}: Error: local label `"98" (instance number 1 of a fb label)' 
> is not defined
> | 
> /home/bermar01/Development/xen-dev/build/profile-fvp-base.prj/tmp/work/fvp_base-poky-linux/xen/4.15+git1-r0/local-xen/xen/xen/Rules.mk:204:
>  recipe for target 'arm64/head.o' failed
>
> This was done adding your 2 patches on top of current staging.
>
> Cheers
> Bertrand
>
> > Cheers,
> >
> > [1] 
> > https://developer.arm.com/support/arm-security-updates/speculative-processor-vulnerability
> > [2] 
> > https://developer.arm.com/support/arm-security-updates/speculative-processor-vulnerability/downloads/straight-line-speculation
> >
> > Julien Grall (2):
> >   xen/arm: Include asm/asm-offsets.h and asm/macros.h on every assembly
> >     files
> >   xen/arm64: Place a speculation barrier following an ret instruction
> >
> > xen/arch/arm/Makefile                |  2 +-
> > xen/arch/arm/arm32/entry.S           |  2 +-
> > xen/arch/arm/arm32/head.S            |  1 -
> > xen/arch/arm/arm32/lib/lib1funcs.S   |  1 +
> > xen/arch/arm/arm32/proc-v7.S         |  1 -
> > xen/arch/arm/arm64/debug-cadence.inc |  1 -
> > xen/arch/arm/arm64/debug-pl011.inc   |  2 --
> > xen/arch/arm/arm64/entry.S           |  2 --
> > xen/arch/arm/arm64/head.S            |  2 --
> > xen/arch/arm/arm64/smc.S             |  3 ---
> > xen/include/asm-arm/arm64/macros.h   |  6 ++++++
> > xen/include/asm-arm/config.h         |  6 ++++++
> > xen/include/asm-arm/macros.h         | 18 +++++++++---------
> > 13 files changed, 24 insertions(+), 23 deletions(-)
> >
> > --
> > 2.17.1
--
Julien Grall