AArch64 emulation ignores SPSel=0 when taking (or returning from) an exception at EL1 or greater

[T McIntosh]

The AArch64 emulation ignores SPSel=0 when:

(1) taking an interrupt from an exception level greater than EL0 (e.g., EL1t),

(2) returning from an exception (via ERET) to an exception level greater than EL0 (e.g., EL1t), with SPSR_ELx[SPSel]=0.

The attached patch fixes the problem in my application.

Background:

I'm running a standalone application (toy OS) that is performing preemptive multithreading between threads running at EL1t, with exception handling / context switching occurring at EL1h. This bug causes the stack pointer to be corrupted in the threads running at EL1t (they end up with a version of the EL1h stack pointer (SP_EL1)).

Occurs in:
 qemu-2.1.0-rc1 (found in)
 commit c60a57ff497667780132a3fcdc1500c83af5d5c0 (current master)

[Edgar E. Iglesias (edgar-iglesias)]

On Mon, Jul 28, 2014 at 07:40:56AM -0000, T McIntosh wrote:
> Public bug reported:
>
> The AArch64 emulation ignores SPSel=0 when:
>
> (1) taking an interrupt from an exception level greater than EL0 (e.g.,
> EL1t),
>
> (2) returning from an exception (via ERET) to an exception level greater
> than EL0 (e.g., EL1t), with SPSR_ELx[SPSel]=0.
>
> The attached patch fixes the problem in my application.

Hi,

Patches 1-3 in the following series fix the this problem.
http://lists.gnu.org/archive/html/qemu-devel/2014-06/msg03675.html

Cheers,
Edgar

[Ubuntu Foundations Team Bug Bot (crichton)]

The attachment "Proposed fix" seems to be a patch. If it isn't, please remove the "patch" flag from the attachment, remove the "patch" tag, and if you are a member of the ~ubuntu-reviewers, unsubscribe the team.

[This is an automated message performed by a Launchpad user owned by ~brian-murray, for any issues please contact him.]

[Chris J Arges (arges)]

Uploaded fixed package for Vivid: https://launchpad.net/ubuntu/+source/qemu/2.1+dfsg-7ubuntu3

Please let me know if this fixes the issue.

[Launchpad Janitor (janitor)]

This bug was fixed in the package qemu - 2.1+dfsg-7ubuntu3

---------------
qemu (2.1+dfsg-7ubuntu3) vivid; urgency=medium

  * d/p/target-arm-A64-Break-out-aarch64_save-restore_sp.patch
    d/p/target-arm-A64-Respect-SPSEL-in-ERET-SP-restore.patch
    d/p/target-arm-A64-Respect-SPSEL-when-taking-exceptions.patch:
    Cherry-pick of upstream patches in order to fix AArch64 emulation ignoring
    SPSel=0 in certain conditions. (LP: #1349277)
 -- Chris J Arges <email address hidden> Thu, 04 Dec 2014 14:17:01 -0600