| Message ID | 5745DA4102000078000EEBF5@prv-mh.provo.novell.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Wed, May 25, 2016 at 09:00:49AM -0600, Jan Beulich wrote: > Correct the number of single byte NOPs we want to be replaced in case > neither SMEP nor SMAP are available. > > Also simplify the expression adding these NOPs - at that location . > equals .Lcr4_orig, and removing that part of the expression fixes a > bogus ".space or fill with negative value, ignored" warning by very old > gas (which actually is what made me look at those constructs again). > > Signed-off-by: Jan Beulich <jbeulich@suse.com> > > --- a/xen/arch/x86/x86_64/compat/entry.S > +++ b/xen/arch/x86/x86_64/compat/entry.S > @@ -175,7 +175,7 @@ compat_bad_hypercall: > ENTRY(compat_restore_all_guest) > ASSERT_INTERRUPTS_DISABLED > .Lcr4_orig: > - .skip (.Lcr4_alt_end - .Lcr4_alt) - (. - .Lcr4_orig), 0x90 > + .skip .Lcr4_alt_end - .Lcr4_alt, 0x90 > .Lcr4_orig_end: > .pushsection .altinstr_replacement, "ax" > .Lcr4_alt: > @@ -200,7 +200,8 @@ ENTRY(compat_restore_all_guest) > jne 1b > .Lcr4_alt_end: > .section .altinstructions, "a" > - altinstruction_entry .Lcr4_orig, .Lcr4_orig, X86_FEATURE_ALWAYS, 12, 0 > + altinstruction_entry .Lcr4_orig, .Lcr4_orig, X86_FEATURE_ALWAYS, \ > + (.Lcr4_orig_end - .Lcr4_orig), 0 > altinstruction_entry .Lcr4_orig, .Lcr4_alt, X86_FEATURE_SMEP, \ > (.Lcr4_orig_end - .Lcr4_orig), \ > (.Lcr4_alt_end - .Lcr4_alt) > > > FWIW: Reviewed-by: Wei Liu <wei.liu2@citrix.com> And subject to review from Andrew: Release-acked-by: Wei Liu <wei.liu2@citrix.com>
On 25/05/16 16:00, Jan Beulich wrote: > Correct the number of single byte NOPs we want to be replaced in case > neither SMEP nor SMAP are available. > > Also simplify the expression adding these NOPs - at that location . > equals .Lcr4_orig, and removing that part of the expression fixes a > bogus ".space or fill with negative value, ignored" warning by very old > gas (which actually is what made me look at those constructs again). > > Signed-off-by: Jan Beulich <jbeulich@suse.com> Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>
>>> On 25.05.16 at 17:00, <JBeulich@suse.com> wrote: > Correct the number of single byte NOPs we want to be replaced in case > neither SMEP nor SMAP are available. > > Also simplify the expression adding these NOPs - at that location . > equals .Lcr4_orig, and removing that part of the expression fixes a > bogus ".space or fill with negative value, ignored" warning by very old > gas (which actually is what made me look at those constructs again). That gas is behaving really strangely: For one, this morning the warning now also appears with the patch in place. I'm sure it wasn't there Wednesday night. Further, warning or not, the generated code is wrong (no NOPs getting inserted at all, obviously resulting in the BUG_ON(a->replacementlen > a->instrlen) in apply_alternatives_nocheck() to trigger during boot). And finally, generated code is right (and the warning gone) when having gas produce a listing via -a. In that case, however, it errors on the four .rept in the hypercall (argument) tables, so we also can't easily use that as a workaround. .list / .nolist don't alter behavior for either of the two issues. I've tried to find some other workaround, but I'm now willing to give up, as there are clearly more useful things to do. We may want / need to consider raising the bar for which binutils versions we support building with. Jan > --- a/xen/arch/x86/x86_64/compat/entry.S > +++ b/xen/arch/x86/x86_64/compat/entry.S > @@ -175,7 +175,7 @@ compat_bad_hypercall: > ENTRY(compat_restore_all_guest) > ASSERT_INTERRUPTS_DISABLED > .Lcr4_orig: > - .skip (.Lcr4_alt_end - .Lcr4_alt) - (. - .Lcr4_orig), 0x90 > + .skip .Lcr4_alt_end - .Lcr4_alt, 0x90 > .Lcr4_orig_end: > .pushsection .altinstr_replacement, "ax" > .Lcr4_alt: > @@ -200,7 +200,8 @@ ENTRY(compat_restore_all_guest) > jne 1b > .Lcr4_alt_end: > .section .altinstructions, "a" > - altinstruction_entry .Lcr4_orig, .Lcr4_orig, X86_FEATURE_ALWAYS, 12, > 0 > + altinstruction_entry .Lcr4_orig, .Lcr4_orig, X86_FEATURE_ALWAYS, \ > + (.Lcr4_orig_end - .Lcr4_orig), 0 > altinstruction_entry .Lcr4_orig, .Lcr4_alt, X86_FEATURE_SMEP, \ > (.Lcr4_orig_end - .Lcr4_orig), \ > (.Lcr4_alt_end - .Lcr4_alt)
--- a/xen/arch/x86/x86_64/compat/entry.S +++ b/xen/arch/x86/x86_64/compat/entry.S @@ -175,7 +175,7 @@ compat_bad_hypercall: ENTRY(compat_restore_all_guest) ASSERT_INTERRUPTS_DISABLED .Lcr4_orig: - .skip (.Lcr4_alt_end - .Lcr4_alt) - (. - .Lcr4_orig), 0x90 + .skip .Lcr4_alt_end - .Lcr4_alt, 0x90 .Lcr4_orig_end: .pushsection .altinstr_replacement, "ax" .Lcr4_alt: @@ -200,7 +200,8 @@ ENTRY(compat_restore_all_guest) jne 1b .Lcr4_alt_end: .section .altinstructions, "a" - altinstruction_entry .Lcr4_orig, .Lcr4_orig, X86_FEATURE_ALWAYS, 12, 0 + altinstruction_entry .Lcr4_orig, .Lcr4_orig, X86_FEATURE_ALWAYS, \ + (.Lcr4_orig_end - .Lcr4_orig), 0 altinstruction_entry .Lcr4_orig, .Lcr4_alt, X86_FEATURE_SMEP, \ (.Lcr4_orig_end - .Lcr4_orig), \ (.Lcr4_alt_end - .Lcr4_alt)