mbox series

[v3,0/2] xen/arm: Mitigate straight-line speculation

Message ID 20210401164444.20377-1-julien@xen.org (mailing list archive)
Headers show
Series xen/arm: Mitigate straight-line speculation | expand

Message

Julien Grall April 1, 2021, 4:44 p.m. UTC 
From: Julien Grall <jgrall@amazon.com>

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.

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(-)