| Date | Wed, 11 May 2022 09:26:51 +0200 | From | Peter Zijlstra <> | Subject | Re: [RFCv2 09/10] x86/mm: Add userspace API to enable Linear Address Masking |
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On Wed, May 11, 2022 at 05:27:50AM +0300, Kirill A. Shutemov wrote: > @@ -1013,8 +1017,23 @@ static long thread_feature_prctl(struct task_struct *task, int option, > > /* Handle ARCH_THREAD_FEATURE_ENABLE */ > > + if (features & (X86_THREAD_LAM_U48 | X86_THREAD_LAM_U57)) { > + long ret; > + > + /* LAM is only available in long mode */ > + if (in_32bit_syscall()) > + return -EINVAL;
So what happens if userspace sets up a 32bit code entry in the LDT and does the LAM thing as a 64bit syscamm but then goes run 32bit code?
> + > + ret = enable_lam(task, features); > + if (ret) > + return ret; > + } > + > task->thread.features |= features; > out: > + /* Update CR3 to get LAM active */ > + switch_mm(task->mm, task->mm, task); > + > return task->thread.features; > } >
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