Re: [PATCH] check smap and !cr0.wp

[Xiao Guangrong <guangrong.xiao@linux.intel.com>]

Hi Paolo,

Could you please apply this patch to kvm-unit-tests if it looks good to you?

Thanks!

On 05/07/2015 04:44 PM, Xiao Guangrong wrote:
> This test case is used to produce the bug that:
>
> KVM may turn a user page to a kernel page when kernel writes a readonly
> user page if CR0.WP = 1. This shadow page entry will be reused after
> SMAP is enabled so that kernel is allowed to access this user page
>
> Signed-off-by: Xiao Guangrong <guangrong.xiao@linux.intel.com>
> ---
>   x86/smap.c | 26 ++++++++++++++++++++++++++
>   1 file changed, 26 insertions(+)
>
> diff --git a/x86/smap.c b/x86/smap.c
> index 042c5aa..66f97b8 100644
> --- a/x86/smap.c
> +++ b/x86/smap.c
> @@ -48,6 +48,7 @@ asm ("pf_tss:\n"
>
>   #define USER_BASE	(1 << 24)
>   #define USER_VAR(v)	(*((__typeof__(&(v))) (((unsigned long)&v) + USER_BASE)))
> +#define USER_ADDR(v)   ((void *)((unsigned long)(&v) + USER_BASE))
>
>   static void init_test(int i)
>   {
> @@ -58,6 +59,29 @@ static void init_test(int i)
>   	}
>   }
>
> +static void check_smap_nowp(void)
> +{
> +	test = 0x99;
> +
> +	*get_pte(phys_to_virt(read_cr3()), USER_ADDR(test)) &= ~PTE_WRITE;
> +
> +	write_cr4(read_cr4() & ~X86_CR4_SMAP);
> +	write_cr0(read_cr0() & ~X86_CR0_WP);
> +	clac();
> +	write_cr3(read_cr3());
> +
> +	init_test(0);
> +	USER_VAR(test) = 0x99;
> +	report("write from user page with SMAP=0, AC=0, WP=0, PTE.U=1 && PTE.W=0", pf_count == 0);
> +
> +	write_cr4(read_cr4() | X86_CR4_SMAP);
> +	write_cr3(read_cr3());
> +
> +	init_test(0);
> +	(void)USER_VAR(test);
> +	report("read from user page with SMAP=1, AC=0, WP=0, PTE.U=1 && PTE.W=0", pf_count == 1 && save == 0x99);
> +}
> +
>   int main(int ac, char **av)
>   {
>   	unsigned long i;
> @@ -150,6 +174,8 @@ int main(int ac, char **av)
>   		report("executing on user page with AC=0", pf_count == 0);
>   	}
>
> +	check_smap_nowp();
> +
>   	// TODO: implicit kernel access from ring 3 (e.g. int)
>
>   	return report_summary();
>