Messages in this thread | | | Date | Tue, 28 Jan 2014 11:35:15 +0800 | From | Ren Qiaowei <> | Subject | Re: [PATCH v3 2/4] x86, mpx: hook #BR exception handler to allocate bound tables |
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On 01/28/2014 04:36 AM, Andy Lutomirski wrote: >> + bd_entry = status & MPX_BNDSTA_ADDR_MASK; >> + if ((bd_entry >= bd_base) && (bd_entry < bd_base + bd_size)) >> + allocate_bt(bd_entry); > > What happens if this fails? Retrying forever isn't very nice. > If allocation of the bound table fail, the related entry in the bound directory is still invalid. The following access to this entry still produce #BR fault.
>> + if (!user_mode(regs)) { >> + if (!fixup_exception(regs)) { >> + tsk->thread.error_code = error_code; >> + tsk->thread.trap_nr = X86_TRAP_BR; >> + die("bounds", regs, error_code); >> + } > > Why the fixup? Unless I'm missing something, the kernel has no business > getting #BR on access to a user address. > > Or are you adding code to allow the kernel to use MPX itself? If so, > shouldn't this use an MPX-specific fixup to allow normal C code to use > this stuff? > It checks whether #BR come from user-space. You can see do_trap_no_signal().
>> + goto exit; >> + } >> + >> + if (!boot_cpu_has(X86_FEATURE_MPX)) { >> + do_trap(X86_TRAP_BR, SIGSEGV, "bounds", regs, error_code, NULL); >> + goto exit; > > This, as well as the status == 0 case, should probably document that the > exception is from BOUND, not MPX. > Ok. I will add one comment for this.
>> + break; >> + >> + case 1: /* Bound violation. */ >> + case 0: /* No MPX exception. */ >> + do_trap(X86_TRAP_BR, SIGSEGV, "bounds", regs, error_code, NULL); >> + break; > > What does "No Intel MPX exception" mean? Surely that has business > sending #BR. > Oh. It comes from spec, and just mean it is not from MPX. :) I will change it to be accurate.
>> + >> + default: >> + break; > > What does status 3 mean? The docs say "reserved". Presumably this > should log and kill the process. I guess it should be a good suggestion.
Thanks, Qiaowei
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