linux/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 Merge branch 'upstream' of git://git.linux-mips.org/pub/scm/ralf/upstream-linus 2016-05-19 10:02:26 -07:00
ar7 MIPS: ar7: use gpiochip data pointer 2016-02-19 09:51:43 +01:00
ath25 genirq: Remove irq argument from irq flow handlers 2015-09-16 15:47:51 +02:00
ath79 TTY and Serial driver update for 4.7-rc1 2016-05-20 20:57:27 -07:00
bcm47xx MIPS: BCM47xx: Move SPROM driver to drivers/firmware/ 2016-05-13 14:01:43 +02:00
bcm63xx Merge branch 'ib-mfd-regulator-gpio-4.6' of git://git.kernel.org/pub/scm/linux/kernel/git/lee/mfd into devel 2016-03-09 17:40:37 +07:00
bmips MIPS: BMIPS: Add support for BCM63268 2016-05-13 14:02:09 +02:00
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 arch/defconfig: remove CONFIG_RESOURCE_COUNTERS 2016-05-23 17:04:14 -07:00
dec MIPS: DEC: Export `ioasic_ssr_lock' to modules 2016-05-17 11:03:54 +02:00
emma
fw MIPS: Fix misspellings in comments. 2016-04-03 12:32:09 +02:00
include MIPS: Fix possible corruption of cache mode by mprotect. 2016-07-02 01:51:39 +02:00
jazz MIPS: Jazz: Migrate to new 'set-state' interface 2015-09-03 12:07:50 +02:00
jz4740 MTD updates for v4.7: 2016-05-24 11:00:20 -07:00
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 MIPS: Change my email address 2016-05-13 14:02:18 +02:00
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 MIPS: Loongson1B: Some updates/fixes for LS1B 2016-05-13 14:02:05 +02:00
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 MIPS: malta-time: Take seconds into account 2016-05-13 15:30:25 +02:00
mti-sead3 MIPS: Introduce plat_get_fdt a platform API to retrieve the FDT 2016-05-13 14:02:03 +02:00
net net: filter: make JITs zero A for SKF_AD_ALU_XOR_X 2016-01-06 00:43:52 -05:00
netlogic MIPS: Define & use CP0_EBase bit definitions 2016-05-13 15:30:25 +02:00
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 Merge branch 'upstream' of git://git.linux-mips.org/pub/scm/ralf/upstream-linus 2016-05-19 10:02:26 -07:00
pistachio MIPS: Pistachio: Enable KASLR 2016-05-28 12:35:11 +02:00
pmcs-msp71xx MIPS: MSP71xx: Use __flush_cache_all instead of flush_cache_all. 2016-05-13 14:01:38 +02:00
pnx833x MIPS: make PCI_DMA_BUS_IS_PHYS=1 constant 2016-05-13 14:02:17 +02:00
power
ralink MIPS: ralink: add MT7628 EPHY LEDs pinmux support 2016-05-28 12:35:05 +02:00
rb532 MIPS: rb532: use gpiochip data pointer 2016-02-19 09:51:44 +01:00
sgi-ip22
sgi-ip27 MIPS: Spelling fix lets -> let's 2016-05-28 12:35:09 +02:00
sgi-ip32
sibyte MIPS: Sibyte: Fix Kconfig dependencies of SIBYTE_BUS_WATCHER 2016-05-09 12:00:03 +02:00
sni MIPS: Spelling fix lets -> let's 2016-05-28 12:35:09 +02:00
txx9 Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net-next 2016-03-19 10:05:34 -07:00
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 Merge branch 'upstream' of git://git.linux-mips.org/pub/scm/ralf/upstream-linus 2015-11-15 09:10:53 -08:00
Kbuild MIPS: Initial implementation of a VDSO 2015-11-11 08:36:36 +01:00
Kbuild.platforms MIPS: Add support for PIC32MZDA platform 2016-01-24 02:53:28 +01:00
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 MIPS: CPS: Early debug using an ns16550-compatible UART 2015-11-11 08:34:25 +01:00
Makefile MIPS: Fix VZ probe gas errors with binutils <2.24 2016-05-17 11:06:04 +02:00