rseq/selftests: arm: use udf instruction for RSEQ_SIG

Use udf as the guard instruction for the restartable sequence abort
handler.

Previously, the chosen signature was not a valid instruction, based
on the assumption that it could always sit in a literal pool. However,
there are compilation environments in which literal pools are not
available, for instance execute-only code. Therefore, we need to
choose a signature value that is also a valid instruction.

Handle compiling with -mbig-endian on ARMv6+, which generates binaries
with mixed code vs data endianness (little endian code, big endian
data).

Else mismatch between code endianness for the generated signatures and
data endianness for the RSEQ_SIG parameter passed to the rseq
registration will trigger application segmentation faults when the
kernel try to abort rseq critical sections.

Prior to ARMv6, -mbig-endian generates big-endian code and data, so
endianness should not be reversed in that case.

Signed-off-by: Mathieu Desnoyers <[email protected]>
CC: Peter Zijlstra <[email protected]>
CC: Thomas Gleixner <[email protected]>
CC: Joel Fernandes <[email protected]>
CC: Catalin Marinas <[email protected]>
CC: Dave Watson <[email protected]>
CC: Will Deacon <[email protected]>
CC: Shuah Khan <[email protected]>
CC: Andi Kleen <[email protected]>
CC: [email protected]
CC: "H . Peter Anvin" <[email protected]>
CC: Chris Lameter <[email protected]>
CC: Russell King <[email protected]>
CC: Michael Kerrisk <[email protected]>
CC: "Paul E . McKenney" <[email protected]>
CC: Paul Turner <[email protected]>
CC: Boqun Feng <[email protected]>
CC: Josh Triplett <[email protected]>
CC: Steven Rostedt <[email protected]>
CC: Ben Maurer <[email protected]>
CC: [email protected]
CC: Andy Lutomirski <[email protected]>
CC: Andrew Morton <[email protected]>
CC: Linus Torvalds <[email protected]>
Signed-off-by: Shuah Khan <[email protected]>

0 files changed, 0 insertions, 0 deletions