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| author | Peter Zijlstra <peterz@infradead.org> | 2019-02-14 12:30:52 +0300 |
|---|---|---|
| committer | Ingo Molnar <mingo@kernel.org> | 2019-04-03 10:36:27 +0300 |
| commit | 6690e86be83ac75832e461c141055b5d601c0a6d (patch) | |
| tree | ac9835c1ef68ed66a41977c0f7f9f788a0b6a6a4 /arch/x86/kernel/process_64.c | |
| parent | 5e7a8ca319268a70a6c7c3c1fde5bea38e1e5539 (diff) | |
| download | linux-6690e86be83ac75832e461c141055b5d601c0a6d.tar.xz | |
sched/x86: Save [ER]FLAGS on context switch
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>
Diffstat (limited to 'arch/x86/kernel/process_64.c')
| -rw-r--r-- | arch/x86/kernel/process_64.c | 8 |
1 files changed, 8 insertions, 0 deletions
diff --git a/arch/x86/kernel/process_64.c b/arch/x86/kernel/process_64.c index 6a62f4af9fcf..026a43be9bd1 100644 --- a/arch/x86/kernel/process_64.c +++ b/arch/x86/kernel/process_64.c @@ -392,6 +392,14 @@ int copy_thread_tls(unsigned long clone_flags, unsigned long sp, childregs = task_pt_regs(p); fork_frame = container_of(childregs, struct fork_frame, regs); frame = &fork_frame->frame; + + /* + * 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; |