hi Aneesh,
On 11/26/18 12:35 PM, Aneesh Kumar K.V wrote:
> With commit 2865d08dd9ea ("powerpc/mm: Move the DSISR_PROTFAULT sanity check")
> we moved the protection fault access check before vma lookup. That means we
> hit that WARN_ON when user space access a kernel address. Before the commit
> this was handled by find_vma() not finding vma for the kernel address and
> considering that access as bad area access.
>
> Avoid the confusing WARN_ON and convert that to a ratelimited printk.
> With the patch we now get
>
> for load:
> [ 187.700294] a.out[5997]: User access of kernel address (c00000000000dea0)
> - exploit attempt? (uid: 1000)
> [ 187.700344] a.out[5997]: segfault (11) at c00000000000dea0 nip 1317c0798
> lr 7fff80d6441c code 1 in a.out[1317c0000+10000]
> [ 187.700429] a.out[5997]: code: 60000000 60420000 3c4c0002 38427790
> 4bffff20 3c4c0002 38427784 fbe1fff8
> [ 187.700435] a.out[5997]: code: f821ffc1 7c3f0b78 60000000 e9228030
> <89290000> 993f002f 60000000 383f0040
>
> for exec:
> [ 225.100903] a.out[6067]: User access of kernel address (c00000000000dea0)
> - exploit attempt? (uid: 1000)
> [ 225.100938] a.out[6067]: segfault (11) at c00000000000dea0 nip
> c00000000000dea0 lr 129d507b0 code 1
> [ 225.100943] a.out[6067]: Bad NIP, not dumping instructions.
>
> Fixes: 2865d08dd9ea ("powerpc/mm: Move the DSISR_PROTFAULT sanity check")
> Signed-off-by: Aneesh Kumar K.V <aneesh.ku...@linux.ibm.com>
Tested-by: Breno Leitao <lei...@debian.org>
> ---
> arch/powerpc/mm/fault.c | 29 ++++++++++++++++++++++++-----
> 1 file changed, 24 insertions(+), 5 deletions(-)
>
> diff --git a/arch/powerpc/mm/fault.c b/arch/powerpc/mm/fault.c
> index 1697e903bbf2..46f280068c45 100644
> --- a/arch/powerpc/mm/fault.c
> +++ b/arch/powerpc/mm/fault.c
> @@ -342,8 +342,21 @@ static inline void cmo_account_page_fault(void) { }
> #endif /* CONFIG_PPC_SMLPAR */
>
> #ifdef CONFIG_PPC_STD_MMU
> -static void sanity_check_fault(bool is_write, unsigned long error_code)
> +static void sanity_check_fault(bool is_write, bool is_user,
> + unsigned long error_code, unsigned long address)
> {
> + /*
> + * userspace trying to access kernel address, we get PROTFAULT for that.
> + */
> + if (is_user && address >= TASK_SIZE) {
> + printk_ratelimited(KERN_CRIT "%s[%d]: "
> + "User access of kernel address (%lx) - "
> + "exploit attempt? (uid: %d)\n",
> + current->comm, current->pid, address,
> + from_kuid(&init_user_ns, current_uid()));
> + return;
Silly question: Is it OK to printk() and just return here? __do_page_fault
will continue to execute independently of this return, right?
