tree 6ef08abfc2e82060af40c487089dc549597949dc
parent a195f3d4528a2f88d6f986f6b1101775ad4891cf
author Peter Zijlstra <peterz@infradead.org> 1603823610 +0100
committer Thomas Gleixner <tglx@linutronix.de> 1603836924 +0100

x86/debug: Fix DR_STEP vs ptrace_get_debugreg(6)

Commit d53d9bc0cf78 ("x86/debug: Change thread.debugreg6 to
thread.virtual_dr6") changed the semantics of the variable from random
collection of bits, to exactly only those bits that ptrace() needs.

Unfortunately this lost DR_STEP for PTRACE_{BLOCK,SINGLE}STEP.

Furthermore, it turns out that userspace expects DR_STEP to be
unconditionally available, even for manual TF usage outside of
PTRACE_{BLOCK,SINGLE}_STEP.

Fixes: d53d9bc0cf78 ("x86/debug: Change thread.debugreg6 to thread.virtual_dr6")
Reported-by: Kyle Huey <me@kylehuey.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Kyle Huey <me@kylehuey.com> 
Link: https://lore.kernel.org/r/20201027183330.GM2628@hirez.programming.kicks-ass.net