On Tue, 1 Aug 2023 at 14:09, Borislav Petkov <bp@xxxxxxxxx> wrote:
>
> On Fri, Jul 28, 2023 at 11:09:08AM +0200, Ard Biesheuvel wrote:
> > diff --git a/arch/x86/boot/compressed/pgtable_64.c b/arch/x86/boot/compressed/pgtable_64.c
> > index 4016444e6788304f..4f50af23a0854f18 100644
> > --- a/arch/x86/boot/compressed/pgtable_64.c
> > +++ b/arch/x86/boot/compressed/pgtable_64.c
> > @@ -101,9 +101,10 @@ static unsigned long find_trampoline_placement(void)
> > return bios_start - TRAMPOLINE_32BIT_SIZE;
> > }
> >
> > -asmlinkage void set_paging_levels(void *rmode)
> > +asmlinkage void set_paging_levels(void *rmode, void *pgtable)
>
> Please get rid of this silly rmode arg which gets passed in here as
> boot_params and then gets assigned to an extern pointer to boot_params.
> This is just silly. Just do what the other functions get from %r15 now
> - a struct boot_params *bp arg.
>
> But perhaps in a separate patch.
>
OK
> > {
> > void (*toggle_la57)(void *trampoline, bool enable_5lvl);
> > + void *trampoline_pgtable;
> > bool l5_required = false;
> >
> > /* Initialize boot_params. Required for cmdline_find_option_bool(). */
> > @@ -133,7 +134,7 @@ asmlinkage void set_paging_levels(void *rmode)
> > * the desired one.
> > */
> > if (l5_required == !!(native_read_cr4() & X86_CR4_LA57))
> > - return;
> > + goto out;
> >
> > trampoline_32bit = (unsigned long *)find_trampoline_placement();
> >
> > @@ -163,6 +164,8 @@ asmlinkage void set_paging_levels(void *rmode)
> > * The new page table will be used by trampoline code for switching
> > * from 4- to 5-level paging or vice versa.
> > */
> > + trampoline_pgtable = trampoline_32bit +
> > + TRAMPOLINE_32BIT_PGTABLE_OFFSET / sizeof(unsigned long);
> >
> > if (l5_required) {
> > /*
> > @@ -182,31 +185,21 @@ asmlinkage void set_paging_levels(void *rmode)
> > * may be above 4G.
> > */
> > src = *(unsigned long *)__native_read_cr3() & PAGE_MASK;
> > - memcpy(trampoline_32bit + TRAMPOLINE_32BIT_PGTABLE_OFFSET / sizeof(unsigned long),
> > - (void *)src, PAGE_SIZE);
> > + memcpy(trampoline_pgtable, (void *)src, PAGE_SIZE);
> > }
> >
> > toggle_la57(trampoline_32bit, l5_required);
> > -}
> > -
> > -void cleanup_trampoline(void *pgtable)
> > -{
> > - void *trampoline_pgtable;
> > -
> > - trampoline_pgtable = trampoline_32bit + TRAMPOLINE_32BIT_PGTABLE_OFFSET / sizeof(unsigned long);
> >
> > /*
> > - * Move the top level page table out of trampoline memory,
> > - * if it's there.
> > + * Move the top level page table out of trampoline memory.
> > */
> > - if ((void *)__native_read_cr3() == trampoline_pgtable) {
> > - memcpy(pgtable, trampoline_pgtable, PAGE_SIZE);
> > - native_write_cr3((unsigned long)pgtable);
> > - }
> > + memcpy(pgtable, trampoline_pgtable, PAGE_SIZE);
> > + native_write_cr3((unsigned long)pgtable);
> >
> > /* Restore trampoline memory */
> > memcpy(trampoline_32bit, trampoline_save, TRAMPOLINE_32BIT_SIZE);
> >
> > +out:
> > /* Initialize variables for 5-level paging */
> > #ifdef CONFIG_X86_5LEVEL
> > if (__read_cr4() & X86_CR4_LA57) {
> > @@ -215,4 +208,5 @@ void cleanup_trampoline(void *pgtable)
> > ptrs_per_p4d = 512;
> > }
> > #endif
> > + return;
>
> No need for that one. It'll return without it. :-)
>
Removing it breaks the build for !CONFIG_X86_5LEVEL
However, I can move these assignments into the conditional at the top
of the function (the one that sets l5_required) so we don't need the
label at all. Will fix for v8
