kernel_optimize_test/arch/mips
Ralf Baechle 6d037de90a MIPS: Fix possible corruption of cache mode by mprotect.
The following testcase may result in a page table entries with a invalid
CCA field being generated:

static void *bindstack;

static int sysrqfd;

static void protect_low(int protect)
{
	mprotect(bindstack, BINDSTACK_SIZE, protect);
}

static void sigbus_handler(int signal, siginfo_t * info, void *context)
{
	void *addr = info->si_addr;

	write(sysrqfd, "x", 1);

	printf("sigbus, fault address %p (should not happen, but might)\n",
	       addr);
	abort();
}

static void run_bind_test(void)
{
	unsigned int *p = bindstack;

	p[0] = 0xf001f001;

	write(sysrqfd, "x", 1);

	/* Set trap on access to p[0] */
	protect_low(PROT_NONE);

	write(sysrqfd, "x", 1);

	/* Clear trap on access to p[0] */
	protect_low(PROT_READ | PROT_WRITE | PROT_EXEC);

	write(sysrqfd, "x", 1);

	/* Check the contents of p[0] */
	if (p[0] != 0xf001f001) {
		write(sysrqfd, "x", 1);

		/* Reached, but shouldn't be */
		printf("badness, shouldn't happen but does\n");
		abort();
	}
}

int main(void)
{
	struct sigaction sa;

	sysrqfd = open("/proc/sysrq-trigger", O_WRONLY);

	if (sigprocmask(SIG_BLOCK, NULL, &sa.sa_mask)) {
		perror("sigprocmask");
		return 0;
	}

	sa.sa_sigaction = sigbus_handler;
	sa.sa_flags = SA_SIGINFO | SA_NODEFER | SA_RESTART;
	if (sigaction(SIGBUS, &sa, NULL)) {
		perror("sigaction");
		return 0;
	}

	bindstack = mmap(NULL,
			 BINDSTACK_SIZE,
			 PROT_READ | PROT_WRITE | PROT_EXEC,
			 MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
	if (bindstack == MAP_FAILED) {
		perror("mmap bindstack");
		return 0;
	}

	printf("bindstack: %p\n", bindstack);

	run_bind_test();

	printf("done\n");

	return 0;
}

There are multiple ingredients for this:

 1) PAGE_NONE is defined to _CACHE_CACHABLE_NONCOHERENT, which is CCA 3
    on all platforms except SB1 where it's CCA 5.
 2) _page_cachable_default must have bits set which are not set
    _CACHE_CACHABLE_NONCOHERENT.
 3) Either the defective version of pte_modify for XPA or the standard
    version must be in used.  However pte_modify for the 36 bit address
    space support is no affected.

In that case additional bits in the final CCA mode may generate an invalid
value for the CCA field.  On the R10000 system where this was tracked
down for example a CCA 7 has been observed, which is Uncached Accelerated.

Fixed by:

 1) Using the proper CCA mode for PAGE_NONE just like for all the other
    PAGE_* pte/pmd bits.
 2) Fix the two affected variants of pte_modify.

Further code inspection also shows the same issue to exist in pmd_modify
which would affect huge page systems.

Issue in pte_modify tracked down by Alastair Bridgewater, PAGE_NONE
and pmd_modify issue found by me.

The history of this goes back beyond Linus' git history.  Chris Dearman's
commit 351336929c ("[MIPS] Allow setting of
the cache attribute at run time.") missed the opportunity to fix this
but it was originally introduced in lmo commit
d523832cf12007b3242e50bb77d0c9e63e0b6518 ("Missing from last commit.")
and 32cc38229ac7538f2346918a09e75413e8861f87 ("New configuration option
CONFIG_MIPS_UNCACHED.")

Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
Reported-by: Alastair Bridgewater <alastair.bridgewater@gmail.com>
2016-07-02 01:51:39 +02:00
..
alchemy
ar7
ath25
ath79
bcm47xx
bcm63xx
bmips
boot MIPS: devicetree: fix cpu interrupt controller node-names 2016-05-28 12:35:12 +02:00
cavium-octeon MIPS: Add missing FROZEN hotplug notifier transitions 2016-05-28 12:35:12 +02:00
cobalt
configs
dec
emma
fw
include MIPS: Fix possible corruption of cache mode by mprotect. 2016-07-02 01:51:39 +02:00
jazz
jz4740
kernel Merge branch 'upstream' of git://git.linux-mips.org/pub/scm/ralf/upstream-linus 2016-05-28 16:41:39 -07:00
kvm MIPS: KVM: Fix CACHE triggered exception emulation 2016-06-14 10:59:45 +02:00
lantiq
lasat MIPS: Lasat: A couple off by one bugs in picvue_proc.c 2016-05-28 12:35:06 +02:00
lib MIPS: lib: Mark intrinsics notrace 2016-05-28 12:35:11 +02:00
loongson32
loongson64 MIPS: Loongson64: Fix typo 2016-05-28 12:35:07 +02:00
math-emu MIPS: math-emu: Fix typo 2016-05-28 12:35:09 +02:00
mm Merge branch 'upstream' of git://git.linux-mips.org/pub/scm/ralf/upstream-linus 2016-05-28 16:41:39 -07:00
mti-malta
mti-sead3
net
netlogic
oprofile MIPS: oprofile: Fix typo 2016-05-28 12:35:09 +02:00
paravirt
pci MIPS: IP27: Fix typo 2016-05-28 12:35:07 +02:00
pic32
pistachio MIPS: Pistachio: Enable KASLR 2016-05-28 12:35:11 +02:00
pmcs-msp71xx
pnx833x
power
ralink MIPS: ralink: add MT7628 EPHY LEDs pinmux support 2016-05-28 12:35:05 +02:00
rb532
sgi-ip22
sgi-ip27 MIPS: Spelling fix lets -> let's 2016-05-28 12:35:09 +02:00
sgi-ip32
sibyte
sni MIPS: Spelling fix lets -> let's 2016-05-28 12:35:09 +02:00
txx9
vdso MIPS: Build microMIPS VDSO for microMIPS kernels 2016-05-28 12:35:12 +02:00
vr41xx MIPS: VR41xx: Fix typo 2016-05-28 12:35:09 +02:00
xilfpga
Kbuild
Kbuild.platforms
Kconfig Merge branch 'upstream' of git://git.linux-mips.org/pub/scm/ralf/upstream-linus 2016-05-28 16:41:39 -07:00
Kconfig.debug
Makefile