Commit 39380b80 authored Jul 08, 2016 by Jiri Kosina Committed by Ingo Molnar Jul 08, 2016

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



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>

parent 946e0f6f

arch/x86/mm/pat.c

+1 −4

Original line number	Diff line number	Diff line
		@@ -755,11 +755,8 @@ static inline int range_is_allowed(unsigned long pfn, unsigned long size)
		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++;
		}

drivers/char/mem.c

+1 −5

Original line number	Diff line number	Diff line
		@@ -66,12 +66,8 @@ static inline int range_is_allowed(unsigned long pfn, unsigned long size)
		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++;
		}

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