[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH v2 2/7] Clear AC bit in RFLAGS to protect Xen itself by SMAP
> -----Original Message----- > From: Jan Beulich [mailto:JBeulich@xxxxxxxx] > Sent: Thursday, April 24, 2014 3:19 PM > To: Wu, Feng > Cc: Andrew Cooper; ian.campbell@xxxxxxxxxx; Dong, Eddie; Nakajima, Jun; Tian, > Kevin; xen-devel@xxxxxxxxxxxxx > Subject: RE: [PATCH v2 2/7] Clear AC bit in RFLAGS to protect Xen itself by > SMAP > > >>> On 24.04.14 at 08:45, <feng.wu@xxxxxxxxx> wrote: > >> From: Andrew Cooper [mailto:andrew.cooper3@xxxxxxxxxx] > >> On 23/04/14 15:35, Feng Wu wrote: > >> > --- a/xen/arch/x86/x86_64/entry.S > >> > +++ b/xen/arch/x86/x86_64/entry.S > >> > @@ -120,6 +120,7 @@ restore_all_xen: > >> > * the space left by the trampoline. > >> > */ > >> > ENTRY(syscall_enter) > >> > + ASM_CLAC > >> > >> Surely this can be sorted more succinctly by setting X86_EFLAGS_AC in > >> MSR 0xc0000084 ? > > > > Okay. > > > >> > >> You also need to patch the entry points in the compat trampoline in > > > > The MSR_SYSCALL_MASK is common in long mode and compat mode, right? > > Seems no need to do anything else for compat mode. > > The same stub is being written there twice, just with different CS > selectors, and both are behind that EFLAGS masking MSR. So I'm not > sure what Andrew's apparently incomplete sentence was actually > intended to mean. Yes, that is also my understanding. > > >> > @@ -268,6 +269,7 @@ bad_hypercall: > >> > jmp test_all_events > >> > > >> > ENTRY(sysenter_entry) > >> > + ASM_CLAC > >> > sti > >> > pushq $FLAT_USER_SS > >> > pushq $0 > > Looking at this again, btw, makes me thing that the clac should go > after the sti here. > > >> > @@ -309,6 +311,7 @@ UNLIKELY_END(sysenter_gpf) > >> > jmp .Lbounce_exception > >> > > >> ... > >> > > >> > .pushsection .init.text, "ax", @progbits > >> > ENTRY(early_page_fault) > >> > + ASM_CLAC > >> > >> I don't think CLAC is appropriate here. This is a pagefault handler for > >> Xen early boot, and is replaced with a real handler substantially before > >> dom0 is created. > > > > Adding CLAC here is not so useful, but harmful neither. If you think it > > should be removed, I will do that in the next post. > > Yes, let's not scatter it around pointlessly (even more so now that > you plan on enabling SMAP only after having built Dom0). > > >> > @@ -689,6 +714,7 @@ ENTRY(enable_nmis) > >> > > >> > /* No op trap handler. Required for kexec crash path. */ > >> > GLOBAL(trap_nop) > >> > + ASM_CLAC > >> > iretq > >> > >> This is not sensible in the slightest, given the following instruction. > > > > The same comments as early_page_fault case. > > The situation is different here, but the addition indeed doesn't seem > to make sense. > > Jan Thanks, Feng _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx http://lists.xen.org/xen-devel
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