From 21266be9ed542f13436bd9c75316d43e1e84f6ae Mon Sep 17 00:00:00 2001 From: Dan Williams Date: Thu, 19 Nov 2015 18:19:29 -0800 Subject: arch: consolidate CONFIG_STRICT_DEVM in lib/Kconfig.debug Let all the archs that implement devmem_is_allowed() opt-in to a common definition of CONFIG_STRICT_DEVM in lib/Kconfig.debug. Cc: Kees Cook Cc: Russell King Cc: Will Deacon Cc: Benjamin Herrenschmidt Cc: Martin Schwidefsky Cc: Thomas Gleixner Cc: "H. Peter Anvin" Cc: Andrew Morton Cc: Greg Kroah-Hartman Cc: "David S. Miller" Acked-by: Catalin Marinas Acked-by: Heiko Carstens [heiko: drop 'default y' for s390] Acked-by: Ingo Molnar Suggested-by: Arnd Bergmann Signed-off-by: Dan Williams --- lib/Kconfig.debug | 22 ++++++++++++++++++++++ 1 file changed, 22 insertions(+) (limited to 'lib') diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug index 8c15b29d5adc..289dfcbc14eb 100644 --- a/lib/Kconfig.debug +++ b/lib/Kconfig.debug @@ -1853,3 +1853,25 @@ source "samples/Kconfig" source "lib/Kconfig.kgdb" +config ARCH_HAS_DEVMEM_IS_ALLOWED + bool + +config STRICT_DEVMEM + bool "Filter access to /dev/mem" + depends on MMU + depends on ARCH_HAS_DEVMEM_IS_ALLOWED + default y if TILE || PPC + ---help--- + If this option is disabled, you allow userspace (root) access to all + of memory, including kernel and userspace memory. Accidental + access to this is obviously disastrous, but specific access can + be used by people debugging the kernel. Note that with PAT support + enabled, even in this case there are restrictions on /dev/mem + use due to the cache aliasing requirements. + + If this option is switched on, the /dev/mem file only allows + userspace access to PCI space and the BIOS code and data regions. + This is sufficient for dosemu and X and all common users of + /dev/mem. + + If in doubt, say Y. -- cgit v1.2.3 From 90a545e981267e917b9d698ce07affd69787db87 Mon Sep 17 00:00:00 2001 From: Dan Williams Date: Mon, 23 Nov 2015 15:49:03 -0800 Subject: restrict /dev/mem to idle io memory ranges This effectively promotes IORESOURCE_BUSY to IORESOURCE_EXCLUSIVE semantics by default. If userspace really believes it is safe to access the memory region it can also perform the extra step of disabling an active driver. This protects device address ranges with read side effects and otherwise directs userspace to use the driver. Persistent memory presents a large "mistake surface" to /dev/mem as now accidental writes can corrupt a filesystem. In general if a device driver is busily using a memory region it already informs other parts of the kernel to not touch it via request_mem_region(). /dev/mem should honor the same safety restriction by default. Debugging a device driver from userspace becomes more difficult with this enabled. Any application using /dev/mem or mmap of sysfs pci resources will now need to perform the extra step of either: 1/ Disabling the driver, for example: echo > /dev/bus//drivers//unbind 2/ Rebooting with "iomem=relaxed" on the command line 3/ Recompiling with CONFIG_IO_STRICT_DEVMEM=n Traditional users of /dev/mem like dosemu are unaffected because the first 1MB of memory is not subject to the IO_STRICT_DEVMEM restriction. Legacy X configurations use /dev/mem to talk to graphics hardware, but that functionality has since moved to kernel graphics drivers. Cc: Arnd Bergmann Cc: Russell King Cc: Andrew Morton Cc: Greg Kroah-Hartman Acked-by: Kees Cook Acked-by: Ingo Molnar Signed-off-by: Dan Williams --- kernel/resource.c | 11 +++++++++-- lib/Kconfig.debug | 23 ++++++++++++++++++++--- 2 files changed, 29 insertions(+), 5 deletions(-) (limited to 'lib') diff --git a/kernel/resource.c b/kernel/resource.c index f150dbbe6f62..09c0597840b0 100644 --- a/kernel/resource.c +++ b/kernel/resource.c @@ -1498,8 +1498,15 @@ int iomem_is_exclusive(u64 addr) break; if (p->end < addr) continue; - if (p->flags & IORESOURCE_BUSY && - p->flags & IORESOURCE_EXCLUSIVE) { + /* + * A resource is exclusive if IORESOURCE_EXCLUSIVE is set + * or CONFIG_IO_STRICT_DEVMEM is enabled and the + * resource is busy. + */ + if ((p->flags & IORESOURCE_BUSY) == 0) + continue; + if (IS_ENABLED(CONFIG_IO_STRICT_DEVMEM) + || p->flags & IORESOURCE_EXCLUSIVE) { err = 1; break; } diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug index 289dfcbc14eb..073496dea848 100644 --- a/lib/Kconfig.debug +++ b/lib/Kconfig.debug @@ -1869,9 +1869,26 @@ config STRICT_DEVMEM enabled, even in this case there are restrictions on /dev/mem use due to the cache aliasing requirements. + If this option is switched on, and IO_STRICT_DEVMEM=n, the /dev/mem + file only allows userspace access to PCI space and the BIOS code and + data regions. This is sufficient for dosemu and X and all common + users of /dev/mem. + + If in doubt, say Y. + +config IO_STRICT_DEVMEM + bool "Filter I/O access to /dev/mem" + depends on STRICT_DEVMEM + default STRICT_DEVMEM + ---help--- + If this option is disabled, you allow userspace (root) access to all + io-memory regardless of whether a driver is actively using that + range. Accidental access to this is obviously disastrous, but + specific access can be used by people debugging kernel drivers. + If this option is switched on, the /dev/mem file only allows - userspace access to PCI space and the BIOS code and data regions. - This is sufficient for dosemu and X and all common users of - /dev/mem. + userspace access to *idle* io-memory ranges (see /proc/iomem) This + may break traditional users of /dev/mem (dosemu, legacy X, etc...) + if the driver using a given range cannot be disabled. If in doubt, say Y. -- cgit v1.2.3