linux-kernel - Re: [PATCH] title: no lookup

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Date:	Mon, 14 Jul 2014 15:35:06 -0400
From:	Chris Metcalf <cmetcalf@...era.com>
To:	Paul Bolle <pebolle@...cali.nl>,
	Nicholas Krause <xerofoify@...il.com>
CC:	<hannes@...xchg.org>, <mhocko@...e.cz>,
	<akpm@...ux-foundation.org>, <zlu@...era.com>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] title: no lookup_page for if statement

On 7/14/2014 2:59 PM, Paul Bolle wrote:
> On Mon, 2014-07-14 at 14:49 -0400, Nicholas Krause wrote:
>> >This patch removes the if define statement for page_lookup in order
>> >to remove a fix me of this not being defined as of yet.
>> >
>> >Signed-off-by: Nicholas Krause<xerofoify@...il.com>

Nicholas, you can't just enable this code; it will break the
build, since there is no lookup_address() symbol on tile.

I'd like to encourage you to look for more substantive kinds of
changes to submit to LKML.  This one and the last one (adding some
underscores to some obsolete symbols) both have ended up costing me
some time to look at and figure out what's actually going on, but
for no real value.  I suspect there may be "janitor" tasks that
are more useful if you are looking for small starting points
(Google for "linux kernel janitors").

That said I'm going to go ahead and check in the following change
which actually does work, now that my attention has been drawn here.

diff --git a/arch/tile/mm/fault.c b/arch/tile/mm/fault.c
index 6c0571216a9d..7e884001ca6a 100644
--- a/arch/tile/mm/fault.c
+++ b/arch/tile/mm/fault.c
@@ -513,17 +513,14 @@ no_context:

         bust_spinlocks(1);

-       /* FIXME: no lookup_address() yet */
-#ifdef SUPPORT_LOOKUP_ADDRESS
-       if (fault_num == INT_ITLB_MISS) {
-               pte_t *pte = lookup_address(address);
+       if (fault_num == INT_ITLB_MISS && address >= PAGE_OFFSET) {
+               pte_t *pte = virt_to_kpte(address);

-               if (pte && pte_present(*pte) && !pte_exec_kernel(*pte))
-                       pr_crit("kernel tried to execute"
-                              " non-executable page - exploit attempt?"
-                              " (uid: %d)\n", current->uid);
+               if (pte && pte_present(*pte) && !pte_exec(*pte))
+                       pr_crit("kernel tried to execute non-executable page"
+                               " - exploit attempt? (uid: %d)\n",
+                               from_kuid(&init_user_ns, current_uid()));
         }
-#endif
         if (address < PAGE_SIZE)
                 pr_alert("Unable to handle kernel NULL pointer dereference\n");
         else

-- 
Chris Metcalf, Tilera Corp.
http://www.tilera.com

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