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

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();
>


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