This is a note to let you know that I've just added the patch titled

x86/mm/pat, /dev/mem: Remove superfluous error message

to the 4.4-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git%3Ba=su...

The filename of the patch is: x86-mm-pat-dev-mem-remove-superfluous-error-message.patch and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let stable@vger.kernel.org know about it.

From 39380b80d72723282f0ea1d1bbf2294eae45013e Mon Sep 17 00:00:00 2001

From: Jiri Kosina jkosina@suse.cz Date: Fri, 8 Jul 2016 11:38:28 +0200 Subject: x86/mm/pat, /dev/mem: Remove superfluous error message

From: Jiri Kosina jkosina@suse.cz

commit 39380b80d72723282f0ea1d1bbf2294eae45013e upstream.

Currently it's possible for broken (or malicious) userspace to flood a kernel log indefinitely with messages a-la

Program dmidecode tried to access /dev/mem between f0000->100000

because range_is_allowed() is case of CONFIG_STRICT_DEVMEM being turned on dumps this information each and every time devmem_is_allowed() fails.

Reportedly userspace that is able to trigger contignuous flow of these messages exists.

It would be possible to rate limit this message, but that'd have a questionable value; the administrator wouldn't get information about all the failing accessess, so then the information would be both superfluous and incomplete at the same time :)

Returning EPERM (which is what is actually happening) is enough indication for userspace what has happened; no need to log this particular error as some sort of special condition.

Signed-off-by: Jiri Kosina jkosina@suse.cz Cc: Andrew Morton akpm@linux-foundation.org Cc: Andy Lutomirski luto@kernel.org Cc: Borislav Petkov bp@alien8.de Cc: Brian Gerst brgerst@gmail.com Cc: Denys Vlasenko dvlasenk@redhat.com Cc: H. Peter Anvin hpa@zytor.com Cc: Josh Poimboeuf jpoimboe@redhat.com Cc: Kees Cook keescook@chromium.org Cc: Linus Torvalds torvalds@linux-foundation.org Cc: Luis R. Rodriguez mcgrof@suse.com Cc: Peter Zijlstra peterz@infradead.org Cc: Thomas Gleixner tglx@linutronix.de Cc: Toshi Kani toshi.kani@hp.com Link: http://lkml.kernel.org/r/alpine.LNX.2.00.1607081137020.24757@cbobk.fhfr.pm Signed-off-by: Ingo Molnar mingo@kernel.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org

--- arch/x86/mm/pat.c | 5 +---- drivers/char/mem.c | 6 +----- 2 files changed, 2 insertions(+), 9 deletions(-)

--- a/arch/x86/mm/pat.c +++ b/arch/x86/mm/pat.c @@ -750,11 +750,8 @@ static inline int range_is_allowed(unsig return 1;

while (cursor < to) { - if (!devmem_is_allowed(pfn)) { - pr_info("x86/PAT: Program %s tried to access /dev/mem between [mem %#010Lx-%#010Lx], PAT prevents it\n", - current->comm, from, to - 1); + if (!devmem_is_allowed(pfn)) return 0; - } cursor += PAGE_SIZE; pfn++; } --- a/drivers/char/mem.c +++ b/drivers/char/mem.c @@ -70,12 +70,8 @@ static inline int range_is_allowed(unsig u64 cursor = from;

while (cursor < to) { - if (!devmem_is_allowed(pfn)) { - printk(KERN_INFO - "Program %s tried to access /dev/mem between %Lx->%Lx.\n", - current->comm, from, to); + if (!devmem_is_allowed(pfn)) return 0; - } cursor += PAGE_SIZE; pfn++; }

Patches currently in stable-queue which might be from jkosina@suse.cz are

queue-4.4/x86-mm-pat-dev-mem-remove-superfluous-error-message.patch