Re: [PATCH 10/13] powerpc: Define KMSAN metadata address ranges for vmalloc and ioremap

[Nicholas Miehlbradt]

On 14/12/2023 8:17 pm, Christophe Leroy wrote:
> Le 14/12/2023 à 06:55, Nicholas Miehlbradt a écrit :
> > Splits the vmalloc region into four. The first quarter is the new
> > vmalloc region, the second is used to store shadow metadata and the
> > third is used to store origin metadata. The fourth quarter is unused.
> >
> > Do the same for the ioremap region.
> >
> > Module data is stored in the vmalloc region so alias the modules
> > metadata addresses to the respective vmalloc metadata addresses. Define
> > MODULES_VADDR and MODULES_END to the start and end of the vmalloc
> > region.
> >
> > Since MODULES_VADDR was previously only defined on ppc32 targets checks
> > for if this macro is defined need to be updated to include
> > defined(CONFIG_PPC32).
>
> Why ?
>
> In your case MODULES_VADDR is above PAGE_OFFSET so there should be no
> difference.
>
> Christophe
On 64 bit builds the BUILD_BUG always triggers since MODULES_VADDR 
expands to __vmalloc_start which is defined in a different translation 
unit. I can restrict the #ifdef CONFIG_PPC32 to just around the 
BUILD_BUG since as you pointed out there is no difference otherwise.
> > Signed-off-by: Nicholas Miehlbradt <nicholas@xxxxxxxxxxxxx>
> > ---
> >    arch/powerpc/include/asm/book3s/64/pgtable.h | 42 ++++++++++++++++++++
> >    arch/powerpc/kernel/module.c                 |  2 +-
> >    2 files changed, 43 insertions(+), 1 deletion(-)
> >
> > diff --git a/arch/powerpc/include/asm/book3s/64/pgtable.h b/arch/powerpc/include/asm/book3s/64/pgtable.h
> > index cb77eddca54b..b3a02b8d96e3 100644
> > --- a/arch/powerpc/include/asm/book3s/64/pgtable.h
> > +++ b/arch/powerpc/include/asm/book3s/64/pgtable.h
> > @@ -249,7 +249,38 @@ enum pgtable_index {
> >    extern unsigned long __vmalloc_start;
> >    extern unsigned long __vmalloc_end;
> >    #define VMALLOC_START	__vmalloc_start
> > +
> > +#ifndef CONFIG_KMSAN
> >    #define VMALLOC_END	__vmalloc_end
> > +#else
> > +/*
> > + * In KMSAN builds vmalloc area is four times smaller, and the remaining 3/4
> > + * are used to keep the metadata for virtual pages. The memory formerly
> > + * belonging to vmalloc area is now laid out as follows:
> > + *
> > + * 1st quarter: VMALLOC_START to VMALLOC_END - new vmalloc area
> > + * 2nd quarter: KMSAN_VMALLOC_SHADOW_START to
> > + *              KMSAN_VMALLOC_SHADOW_START+VMALLOC_LEN - vmalloc area shadow
> > + * 3rd quarter: KMSAN_VMALLOC_ORIGIN_START to
> > + *              KMSAN_VMALLOC_ORIGIN_START+VMALLOC_LEN - vmalloc area origins
> > + * 4th quarter: unused
> > + */
> > +#define VMALLOC_LEN ((__vmalloc_end - __vmalloc_start) >> 2)
> > +#define VMALLOC_END (VMALLOC_START + VMALLOC_LEN)
> > +
> > +#define KMSAN_VMALLOC_SHADOW_START VMALLOC_END
> > +#define KMSAN_VMALLOC_ORIGIN_START (VMALLOC_END + VMALLOC_LEN)
> > +
> > +/*
> > + * Module metadata is stored in the corresponding vmalloc metadata regions
> > + */
> > +#define KMSAN_MODULES_SHADOW_START	KMSAN_VMALLOC_SHADOW_START
> > +#define KMSAN_MODULES_ORIGIN_START	KMSAN_VMALLOC_ORIGIN_START
> > +#endif /* CONFIG_KMSAN */
> > +
> > +#define MODULES_VADDR VMALLOC_START
> > +#define MODULES_END VMALLOC_END
> > +#define MODULES_LEN		(MODULES_END - MODULES_VADDR)
> >    
> >    static inline unsigned int ioremap_max_order(void)
> >    {
> > @@ -264,7 +295,18 @@ extern unsigned long __kernel_io_start;
> >    extern unsigned long __kernel_io_end;
> >    #define KERN_VIRT_START __kernel_virt_start
> >    #define KERN_IO_START  __kernel_io_start
> > +#ifndef CONFIG_KMSAN
> >    #define KERN_IO_END __kernel_io_end
> > +#else
> > +/*
> > + * In KMSAN builds IO space is 4 times smaller, the remaining space is used to
> > + * store metadata. See comment for vmalloc regions above.
> > + */
> > +#define KERN_IO_LEN             ((__kernel_io_end - __kernel_io_start) >> 2)
> > +#define KERN_IO_END             (KERN_IO_START + KERN_IO_LEN)
> > +#define KERN_IO_SHADOW_START    KERN_IO_END
> > +#define KERN_IO_ORIGIN_START    (KERN_IO_SHADOW_START + KERN_IO_LEN)
> > +#endif /* !CONFIG_KMSAN */
> >    
> >    extern struct page *vmemmap;
> >    extern unsigned long pci_io_base;
> > diff --git a/arch/powerpc/kernel/module.c b/arch/powerpc/kernel/module.c
> > index f6d6ae0a1692..5043b959ad4d 100644
> > --- a/arch/powerpc/kernel/module.c
> > +++ b/arch/powerpc/kernel/module.c
> > @@ -107,7 +107,7 @@ __module_alloc(unsigned long size, unsigned long start, unsigned long end, bool
> >    
> >    void *module_alloc(unsigned long size)
> >    {
> > -#ifdef MODULES_VADDR
> > +#if defined(MODULES_VADDR) && defined(CONFIG_PPC32)
> >    	unsigned long limit = (unsigned long)_etext - SZ_32M;
> >    	void *ptr = NULL;
> >