diff options
| author | Peter Zijlstra <peterz@infradead.org> | 2019-02-14 10:30:52 +0100 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2019-05-21 18:50:14 +0200 |
| commit | 2373ac080fa336e04af2000506ad701a515ce527 (patch) | |
| tree | 479dce9757007416a3288b186dfe7ddf5ed12ff1 /arch/x86/kernel/process_32.c | |
| parent | dffad3e47c5ae36046b8275f158bad959a27d534 (diff) | |
sched/x86: Save [ER]FLAGS on context switch
commit 6690e86be83ac75832e461c141055b5d601c0a6d upstream.
Effectively reverts commit:
2c7577a75837 ("sched/x86_64: Don't save flags on context switch")
Specifically because SMAP uses FLAGS.AC which invalidates the claim
that the kernel has clean flags.
In particular; while preemption from interrupt return is fine (the
IRET frame on the exception stack contains FLAGS) it breaks any code
that does synchonous scheduling, including preempt_enable().
This has become a significant issue ever since commit:
5b24a7a2aa20 ("Add 'unsafe' user access functions for batched accesses")
provided for means of having 'normal' C code between STAC / CLAC,
exposing the FLAGS.AC state. So far this hasn't led to trouble,
however fix it before it comes apart.
Reported-by: Julien Thierry <julien.thierry@arm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: stable@kernel.org
Fixes: 5b24a7a2aa20 ("Add 'unsafe' user access functions for batched accesses")
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'arch/x86/kernel/process_32.c')
| -rw-r--r-- | arch/x86/kernel/process_32.c | 7 |
1 files changed, 7 insertions, 0 deletions
diff --git a/arch/x86/kernel/process_32.c b/arch/x86/kernel/process_32.c index c2df91eab573..df6bb5f8ab2a 100644 --- a/arch/x86/kernel/process_32.c +++ b/arch/x86/kernel/process_32.c @@ -132,6 +132,13 @@ int copy_thread_tls(unsigned long clone_flags, unsigned long sp, struct task_struct *tsk; int err; + /* + * For a new task use the RESET flags value since there is no before. + * All the status flags are zero; DF and all the system flags must also + * be 0, specifically IF must be 0 because we context switch to the new + * task with interrupts disabled. + */ + frame->flags = X86_EFLAGS_FIXED; frame->bp = 0; frame->ret_addr = (unsigned long) ret_from_fork; p->thread.sp = (unsigned long) fork_frame; |