On Tue, Jul 30, 2019 at 12:12:54PM -0700, Thomas Garnier wrote: > if PIE is enabled, switch the paravirt assembly constraints to be > compatible. The %c/i constrains generate smaller code so is kept by > default. > > Position Independent Executable (PIE) support will allow to extend the > KASLR randomization range below 0xffffffff80000000. > > Signed-off-by: Thomas Garnier <thgar...@chromium.org> > Acked-by: Juergen Gross <jgr...@suse.com> > --- > arch/x86/include/asm/paravirt_types.h | 25 +++++++++++++++++++++---- > 1 file changed, 21 insertions(+), 4 deletions(-) > > diff --git a/arch/x86/include/asm/paravirt_types.h > b/arch/x86/include/asm/paravirt_types.h > index 70b654f3ffe5..fd7dc37d0010 100644 > --- a/arch/x86/include/asm/paravirt_types.h > +++ b/arch/x86/include/asm/paravirt_types.h > @@ -338,9 +338,25 @@ extern struct paravirt_patch_template pv_ops; > #define PARAVIRT_PATCH(x) \ > (offsetof(struct paravirt_patch_template, x) / sizeof(void *)) > > +#ifdef CONFIG_X86_PIE > +#define paravirt_opptr_call "a" > +#define paravirt_opptr_type "p" > + > +/* > + * Alternative patching requires a maximum of 7 bytes but the relative call > is > + * only 6 bytes. If PIE is enabled, add an additional nop to the call > + * instruction to ensure patching is possible. > + */ > +#define PARAVIRT_CALL_POST "nop;"
I'm confused; where does the 7 come from? The relative call is 6 bytes, a normal call is 5 bytes (which is what we normally replace them with), and the longest 'native' sequence we seem to have is also 6 bytes (.cpu_usergs_sysret64). > +#else > +#define paravirt_opptr_call "c" > +#define paravirt_opptr_type "i" > +#define PARAVIRT_CALL_POST "" > +#endif > + > #define paravirt_type(op) \ > [paravirt_typenum] "i" (PARAVIRT_PATCH(op)), \ > - [paravirt_opptr] "i" (&(pv_ops.op)) > + [paravirt_opptr] paravirt_opptr_type (&(pv_ops.op)) > #define paravirt_clobber(clobber) \ > [paravirt_clobber] "i" (clobber) > > @@ -379,9 +395,10 @@ int paravirt_disable_iospace(void); > * offset into the paravirt_patch_template structure, and can therefore be > * freely converted back into a structure offset. > */ > -#define PARAVIRT_CALL \ > - ANNOTATE_RETPOLINE_SAFE \ > - "call *%c[paravirt_opptr];" > +#define PARAVIRT_CALL \ > + ANNOTATE_RETPOLINE_SAFE \ > + "call *%" paravirt_opptr_call "[paravirt_opptr];" \ > + PARAVIRT_CALL_POST
