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Date: Mon, 27 Oct 2014 02:17:58 +0000 From: "Ren, Qiaowei" <qiaowei.ren@...el.com> To: Thomas Gleixner <tglx@...utronix.de> CC: "H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...hat.com>, "Hansen, Dave" <dave.hansen@...el.com>, "x86@...nel.org" <x86@...nel.org>, "linux-mm@...ck.org" <linux-mm@...ck.org>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, "linux-ia64@...r.kernel.org" <linux-ia64@...r.kernel.org>, "linux-mips@...ux-mips.org" <linux-mips@...ux-mips.org> Subject: RE: [PATCH v9 10/12] x86, mpx: add prctl commands PR_MPX_ENABLE_MANAGEMENT, PR_MPX_DISABLE_MANAGEMENT On 2014-10-24, Thomas Gleixner wrote: > On Sun, 12 Oct 2014, Qiaowei Ren wrote: >> +int mpx_enable_management(struct task_struct *tsk) { >> + struct mm_struct *mm = tsk->mm; >> + void __user *bd_base = MPX_INVALID_BOUNDS_DIR; > > What's the point of initializing bd_base here. I had to look twice to > figure out that it gets overwritten by task_get_bounds_dir() > I just want to put task_get_bounds_dir() outside mm->mmap_sem holding. >> @@ -285,6 +285,7 @@ dotraplinkage void do_bounds(struct pt_regs >> *regs, > long error_code) >> struct xsave_struct *xsave_buf; >> struct task_struct *tsk = current; >> siginfo_t info; >> + int ret = 0; >> >> prev_state = exception_enter(); >> if (notify_die(DIE_TRAP, "bounds", regs, error_code, @@ -312,8 >> +313,35 @@ dotraplinkage void do_bounds(struct pt_regs *regs, long > error_code) >> */ >> switch (status & MPX_BNDSTA_ERROR_CODE) { >> case 2: /* Bound directory has invalid entry. */ >> - if (do_mpx_bt_fault(xsave_buf)) >> + down_write(¤t->mm->mmap_sem); > > The handling of mm->mmap_sem here is horrible. The only reason why you > want to hold mmap_sem write locked in the first place is that you want > to cover the allocation and the mm->bd_addr check. > > I think it's wrong to tie this to mmap_sem in the first place. If MPX > is enabled then you should have mm->bd_addr and an explicit mutex to protect it. > > So the logic would look like this: > > mutex_lock(&mm->bd_mutex); > if (!kernel_managed(mm)) > do_trap(); else if (do_mpx_bt_fault()) force_sig(); > mutex_unlock(&mm->bd_mutex); > No tricks with mmap_sem, no special return value handling. Straight > forward code instead of a convoluted and error prone mess. > > Hmm? > I guess this is a good solution. If so, new field 'bd_sem' have to be added into struct mm_struct. Thanks, Qiaowei -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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