Re: [PATCH 2/5] x86, pti: fix boot warning from Global-bit setting

Aaro Koskinen
2018-04-23T10:51:38Z

Hi,

On Fri, Apr 20, 2018 at 03:20:21PM -0700, Dave Hansen wrote:
> The pageattr.c code attempts to process "faults" when it goes looking
> for PTEs to change and finds non-present entries. It allows these
> faults in the linear map which is "expected to have holes", but
> WARN()s about them elsewhere, like when called on the kernel image.
>
> However, we are now calling change_page_attr_clear() on the kernel
> image in the process of trying to clear the Global bit.
>
> This trips the warning in __cpa_process_fault() if a non-present PTE is
> encountered in the kernel image. The "holes" in the kernel image
> result from free_init_pages()'s use of set_memory_np(). These holes
> are totally fine, and result from normal operation, just as they would
> be in the kernel linear map.
>
> Just silence the warning when holes in the kernel image are encountered.
>
> Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
> Fixes: 39114b7a7 (x86/pti: Never implicitly clear _PAGE_GLOBAL for kernel image)
> Reported-by: Mariusz Ceier <mceier@gmail.com>
> Reported-by: Aaro Koskinen <aaro.koskinen@nokia.com>

Tested-by: Aaro Koskinen <aaro.koskinen@nokia.com>

A.

> Cc: Andrea Arcangeli <aarcange@redhat.com>
> Cc: Andy Lutomirski <luto@kernel.org>
> Cc: Arjan van de Ven <arjan@linux.intel.com>
> Cc: Borislav Petkov <bp@alien8.de>
> Cc: Dan Williams <dan.j.williams@intel.com>
> Cc: David Woodhouse <dwmw2@infradead.org>
> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> Cc: Hugh Dickins <hughd@google.com>
> Cc: Josh Poimboeuf <jpoimboe@redhat.com>
> Cc: Juergen Gross <jgross@suse.com>
> Cc: Kees Cook <keescook@google.com>
> Cc: Linus Torvalds <torvalds@linux-foundation.org>
> Cc: Nadav Amit <namit@vmware.com>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: linux-mm@kvack.org
> ---
>
> b/arch/x86/mm/pageattr.c | 41 +++++++++++++++++++++++++++++++----------
> 1 file changed, 31 insertions(+), 10 deletions(-)
>
> diff -puN arch/x86/mm/pageattr.c~pti-glb-warning-inpageattr arch/x86/mm/pageattr.c
> --- a/arch/x86/mm/pageattr.c~pti-glb-warning-inpageattr 2018-04-20 14:10:01.619749168 -0700
> +++ b/arch/x86/mm/pageattr.c 2018-04-20 14:10:01.623749168 -0700
> @@ -93,6 +93,18 @@ void arch_report_meminfo(struct seq_file
> static inline void split_page_count(int level) { }
> #endif
>
> +static inline int
> +within(unsigned long addr, unsigned long start, unsigned long end)
> +{
> + return addr >= start && addr < end;
> +}
> +
> +static inline int
> +within_inclusive(unsigned long addr, unsigned long start, unsigned long end)
> +{
> + return addr >= start && addr <= end;
> +}
> +
> #ifdef CONFIG_X86_64
>
> static inline unsigned long highmap_start_pfn(void)
> @@ -106,20 +118,26 @@ static inline unsigned long highmap_end_
> return __pa_symbol(roundup(_brk_end, PMD_SIZE) - 1) >> PAGE_SHIFT;
> }
>
> -#endif
> -
> -static inline int
> -within(unsigned long addr, unsigned long start, unsigned long end)
> +static bool __cpa_pfn_in_highmap(unsigned long pfn)
> {
> - return addr >= start && addr < end;
> + /*
> + * Kernel text has an alias mapping at a high address, known
> + * here as "highmap".
> + */
> + return within_inclusive(pfn, highmap_start_pfn(),
> + highmap_end_pfn());
> }
>
> -static inline int
> -within_inclusive(unsigned long addr, unsigned long start, unsigned long end)
> +#else
> +
> +static bool __cpa_pfn_in_highmap(unsigned long pfn)
> {
> - return addr >= start && addr <= end;
> + /* There is no highmap on 32-bit */
> + return false;
> }
>
> +#endif
> +
> /*
> * Flushing functions
> */
> @@ -1183,6 +1201,10 @@ static int __cpa_process_fault(struct cp
> cpa->numpages = 1;
> cpa->pfn = __pa(vaddr) >> PAGE_SHIFT;
> return 0;
> +
> + } else if (__cpa_pfn_in_highmap(cpa->pfn)) {
> + /* Faults in the highmap are OK, so do not warn: */
> + return -EFAULT;
> } else {
> WARN(1, KERN_WARNING "CPA: called for zero pte. "
> "vaddr = %lx cpa->vaddr = %lx\n", vaddr,
> @@ -1335,8 +1357,7 @@ static int cpa_process_alias(struct cpa_
> * to touch the high mapped kernel as well:
> */
> if (!within(vaddr, (unsigned long)_text, _brk_end) &&
> - within_inclusive(cpa->pfn, highmap_start_pfn(),
> - highmap_end_pfn())) {
> + __cpa_pfn_in_highmap(cpa->pfn)) {
> unsigned long temp_cpa_vaddr = (cpa->pfn << PAGE_SHIFT) +
> __START_KERNEL_map - phys_base;
> alias_cpa = *cpa;
> _