Re: [PATCH 2/4] arch/x86: implement the process_vm_exec syscall
flat view
From: Jann Horn <jannh@google.com>
Date: 2021-06-28 16:14:01
Also in:
linux-um, lkml
On Wed, Apr 14, 2021 at 7:59 AM Andrei Vagin [off-list ref] wrote:
This change introduces the new system call:
process_vm_exec(pid_t pid, struct sigcontext *uctx, unsigned long flags,
siginfo_t * uinfo, sigset_t *sigmask, size_t sizemask)
process_vm_exec allows to execute the current process in an address
space of another process.[...] I still think that this whole API is fundamentally the wrong approach because it tries to shoehorn multiple usecases with different requirements into a single API. But that aside:
quoted hunk ↗ jump to hunk
+static void swap_mm(struct mm_struct *prev_mm, struct mm_struct *target_mm) +{ + struct task_struct *tsk = current; + struct mm_struct *active_mm; + + task_lock(tsk); + /* Hold off tlb flush IPIs while switching mm's */ + local_irq_disable(); + + sync_mm_rss(prev_mm); + + vmacache_flush(tsk); + + active_mm = tsk->active_mm; + if (active_mm != target_mm) { + mmgrab(target_mm); + tsk->active_mm = target_mm; + } + tsk->mm = target_mm;
I'm pretty sure you're not currently allowed to overwrite the ->mm pointer of a userspace thread. For example, zap_threads() assumes that all threads running under a process have the same ->mm. (And if you're fiddling with ->mm stuff, you should probably CC linux-mm@.) As far as I understand, only kthreads are allowed to do this (as implemented in kthread_use_mm()).
quoted hunk ↗ jump to hunk
+ switch_mm_irqs_off(active_mm, target_mm, tsk); + local_irq_enable(); + task_unlock(tsk); +#ifdef finish_arch_post_lock_switch + finish_arch_post_lock_switch(); +#endif + + if (active_mm != target_mm) + mmdrop(active_mm); +}