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Message-ID: <CAGXu5jL1BBAvoxVqFa1YHJSMCbGdLiPey-dyC15YKVPB2xGfig@mail.gmail.com> Date: Tue, 4 Nov 2014 10:43:00 -0800 From: Kees Cook <keescook@...omium.org> To: Leif Lindholm <leif.lindholm@...aro.org> Cc: LKML <linux-kernel@...r.kernel.org>, "linux-arm-kernel@...ts.infradead.org" <linux-arm-kernel@...ts.infradead.org>, linuxppc-dev@...ts.ozlabs.org, linux-s390@...r.kernel.org, Russell King - ARM Linux <linux@....linux.org.uk>, Catalin Marinas <catalin.marinas@....com>, Will Deacon <will.deacon@....com>, "benh@...nel.crashing.org" <benh@...nel.crashing.org>, paulus@...ba.org, mpe@...erman.id.au, Martin Schwidefsky <schwidefsky@...ibm.com>, eiko.carstens@...ibm.com, linux390@...ibm.com, metcalf@...era.com, Guan Xuetao <gxt@...c.pku.edu.cn>, Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, "H. Peter Anvin" <hpa@...or.com>, "x86@...nel.org" <x86@...nel.org>, Arnd Bergmann <arnd@...db.de>, Greg KH <gregkh@...uxfoundation.org>, Andy Lutomirski <luto@...capital.net>, Oleg Nesterov <oleg@...hat.com>, Andrew Morton <akpm@...ux-foundation.org>, dave.long@...aro.org, Christoph Hellwig <hch@...radead.org>, Arjan van de Ven <arjan@...ux.intel.com> Subject: Re: [RFC PATCH] make CONFIG_STRICT_DEVMEM a core non-debug feature On Tue, Nov 4, 2014 at 9:23 AM, Leif Lindholm <leif.lindholm@...aro.org> wrote: > Most, but not all, architectures supporting CONFIG_STRICT_DEVMEM treat > it as a debug feature - although its function is pretty much the > opposite of debug. > > This patch deletes all architecture-specific config options and moves > the option to core code, as a non-debug option. > > Signed-off-by: Leif Lindholm <leif.lindholm@...aro.org> > --- > Apologies for wide distribution, but this is a bit invasive, > if trivial. > > arch/Kconfig | 3 +++ > arch/arm/Kconfig | 1 + > arch/arm/Kconfig.debug | 14 -------------- > arch/arm64/Kconfig | 1 + > arch/arm64/Kconfig.debug | 14 -------------- > arch/powerpc/Kconfig | 1 + > arch/powerpc/Kconfig.debug | 12 ------------ > arch/s390/Kconfig | 1 + > arch/s390/Kconfig.debug | 12 ------------ > arch/tile/Kconfig | 4 +--- > arch/unicore32/Kconfig | 1 + > arch/unicore32/Kconfig.debug | 14 -------------- > arch/x86/Kconfig | 1 + > arch/x86/Kconfig.debug | 17 ----------------- > drivers/char/Kconfig | 16 ++++++++++++++++ > 15 files changed, 26 insertions(+), 86 deletions(-) > > diff --git a/arch/Kconfig b/arch/Kconfig > index 05d7a8a..e5f4f03 100644 > --- a/arch/Kconfig > +++ b/arch/Kconfig > @@ -484,6 +484,9 @@ config HAVE_IRQ_EXIT_ON_IRQ_STACK > This spares a stack switch and improves cache usage on softirq > processing. > > +config HAVE_ARCH_RESTRICTED_DEVMEM > + bool > + > # > # ABI hall of shame > # > diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig > index 89c4b5c..e04910f 100644 > --- a/arch/arm/Kconfig > +++ b/arch/arm/Kconfig > @@ -30,6 +30,7 @@ config ARM > select HAVE_ARCH_AUDITSYSCALL if (AEABI && !OABI_COMPAT) > select HAVE_ARCH_JUMP_LABEL if !XIP_KERNEL > select HAVE_ARCH_KGDB > + select HAVE_ARCH_RESTRICTED_DEVMEM if MMU > select HAVE_ARCH_SECCOMP_FILTER if (AEABI && !OABI_COMPAT) > select HAVE_ARCH_TRACEHOOK > select HAVE_BPF_JIT > diff --git a/arch/arm/Kconfig.debug b/arch/arm/Kconfig.debug > index d8f6a2e..2a02a7d 100644 > --- a/arch/arm/Kconfig.debug > +++ b/arch/arm/Kconfig.debug > @@ -14,20 +14,6 @@ config ARM_PTDUMP > kernel. > If in doubt, say "N" > > -config STRICT_DEVMEM > - bool "Filter access to /dev/mem" > - depends on MMU > - ---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. > - > - If this option is switched on, the /dev/mem file only allows > - userspace access to memory mapped peripherals. > - > - If in doubt, say Y. > - > # RMK wants arm kernels compiled with frame pointers or stack unwinding. > # If you know what you are doing and are willing to live without stack > # traces, you can get a slightly smaller kernel by setting this option to > diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig > index 9532f8d..90abbb2 100644 > --- a/arch/arm64/Kconfig > +++ b/arch/arm64/Kconfig > @@ -37,6 +37,7 @@ config ARM64 > select HAVE_ARCH_AUDITSYSCALL > select HAVE_ARCH_JUMP_LABEL > select HAVE_ARCH_KGDB > + select HAVE_ARCH_RESTRICTED_DEVMEM if MMU > select HAVE_ARCH_TRACEHOOK > select HAVE_BPF_JIT > select HAVE_C_RECORDMCOUNT > diff --git a/arch/arm64/Kconfig.debug b/arch/arm64/Kconfig.debug > index 0a12933..d0036dd 100644 > --- a/arch/arm64/Kconfig.debug > +++ b/arch/arm64/Kconfig.debug > @@ -6,20 +6,6 @@ config FRAME_POINTER > bool > default y > > -config STRICT_DEVMEM > - bool "Filter access to /dev/mem" > - depends on MMU > - 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. > - > - If this option is switched on, the /dev/mem file only allows > - userspace access to memory mapped peripherals. > - > - If in doubt, say Y. > - > config PID_IN_CONTEXTIDR > bool "Write the current PID to the CONTEXTIDR register" > help > diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig > index 88eace4..cd35068 100644 > --- a/arch/powerpc/Kconfig > +++ b/arch/powerpc/Kconfig > @@ -148,6 +148,7 @@ config PPC > select HAVE_ARCH_AUDITSYSCALL > select ARCH_SUPPORTS_ATOMIC_RMW > select DCACHE_WORD_ACCESS if PPC64 && CPU_LITTLE_ENDIAN > + select HAVE_ARCH_RESTRICTED_DEVMEM > > config GENERIC_CSUM > def_bool CPU_LITTLE_ENDIAN > diff --git a/arch/powerpc/Kconfig.debug b/arch/powerpc/Kconfig.debug > index ec2e40f..6f11382 100644 > --- a/arch/powerpc/Kconfig.debug > +++ b/arch/powerpc/Kconfig.debug > @@ -334,18 +334,6 @@ config PPC_EARLY_DEBUG_CPM_ADDR > platform probing is done, all platforms selected must > share the same address. > > -config STRICT_DEVMEM > - def_bool y > - prompt "Filter access to /dev/mem" > - help > - This option restricts access to /dev/mem. If this option is > - disabled, you allow userspace access to all memory, including > - kernel and userspace memory. Accidental memory access is likely > - to be disastrous. > - Memory access is required for experts who want to debug the kernel. > - > - If you are unsure, say Y. > - > config FAIL_IOMMU > bool "Fault-injection capability for IOMMU" > depends on FAULT_INJECTION > diff --git a/arch/s390/Kconfig b/arch/s390/Kconfig > index f2cf1f9..fe92272 100644 > --- a/arch/s390/Kconfig > +++ b/arch/s390/Kconfig > @@ -109,6 +109,7 @@ config S390 > select HAVE_ALIGNED_STRUCT_PAGE if SLUB > select HAVE_ARCH_AUDITSYSCALL > select HAVE_ARCH_JUMP_LABEL if !MARCH_G5 > + select HAVE_ARCH_RESTRICTED_DEVMEM > select HAVE_ARCH_SECCOMP_FILTER > select HAVE_ARCH_TRACEHOOK > select HAVE_ARCH_TRANSPARENT_HUGEPAGE if 64BIT > diff --git a/arch/s390/Kconfig.debug b/arch/s390/Kconfig.debug > index c56878e..26c5d5be 100644 > --- a/arch/s390/Kconfig.debug > +++ b/arch/s390/Kconfig.debug > @@ -5,18 +5,6 @@ config TRACE_IRQFLAGS_SUPPORT > > source "lib/Kconfig.debug" > > -config STRICT_DEVMEM > - def_bool y > - prompt "Filter access to /dev/mem" > - ---help--- > - This option restricts access to /dev/mem. If this option is > - disabled, you allow userspace access to all memory, including > - kernel and userspace memory. Accidental memory access is likely > - to be disastrous. > - Memory access is required for experts who want to debug the kernel. > - > - If you are unsure, say Y. > - > config S390_PTDUMP > bool "Export kernel pagetable layout to userspace via debugfs" > depends on DEBUG_KERNEL > diff --git a/arch/tile/Kconfig b/arch/tile/Kconfig > index 7cca418..f881168 100644 > --- a/arch/tile/Kconfig > +++ b/arch/tile/Kconfig > @@ -27,6 +27,7 @@ config TILE > select ARCH_HAS_ATOMIC64_DEC_IF_POSITIVE > select HAVE_DEBUG_STACKOVERFLOW > select ARCH_WANT_FRAME_POINTERS > + select HAVE_ARCH_RESTRICTED_DEVMEM > > # FIXME: investigate whether we need/want these options. > # select HAVE_IOREMAP_PROT > @@ -110,9 +111,6 @@ config ARCH_DISCONTIGMEM_DEFAULT > config TRACE_IRQFLAGS_SUPPORT > def_bool y > > -config STRICT_DEVMEM > - def_bool y > - > # SMP is required for Tilera Linux. > config SMP > def_bool y > diff --git a/arch/unicore32/Kconfig b/arch/unicore32/Kconfig > index 928237a..574b07f 100644 > --- a/arch/unicore32/Kconfig > +++ b/arch/unicore32/Kconfig > @@ -18,6 +18,7 @@ config UNICORE32 > select ARCH_WANT_FRAME_POINTERS > select GENERIC_IOMAP > select MODULES_USE_ELF_REL > + select HAVE_ARCH_RESTRICTED_DEVMEM if MMU > help > UniCore-32 is 32-bit Instruction Set Architecture, > including a series of low-power-consumption RISC chip > diff --git a/arch/unicore32/Kconfig.debug b/arch/unicore32/Kconfig.debug > index 1a36262..f075bbe 100644 > --- a/arch/unicore32/Kconfig.debug > +++ b/arch/unicore32/Kconfig.debug > @@ -2,20 +2,6 @@ menu "Kernel hacking" > > source "lib/Kconfig.debug" > > -config STRICT_DEVMEM > - bool "Filter access to /dev/mem" > - depends on MMU > - ---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. > - > - If this option is switched on, the /dev/mem file only allows > - userspace access to memory mapped peripherals. > - > - If in doubt, say Y. > - > config EARLY_PRINTK > def_bool DEBUG_OCD > help > diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig > index ded8a67..91392bf 100644 > --- a/arch/x86/Kconfig > +++ b/arch/x86/Kconfig > @@ -137,6 +137,7 @@ config X86 > select HAVE_ACPI_APEI_NMI if ACPI > select ACPI_LEGACY_TABLES_LOOKUP if ACPI > select X86_FEATURE_NAMES if PROC_FS > + select HAVE_ARCH_RESTRICTED_DEVMEM > > config INSTRUCTION_DECODER > def_bool y > diff --git a/arch/x86/Kconfig.debug b/arch/x86/Kconfig.debug > index 61bd2ad..e35d4a1 100644 > --- a/arch/x86/Kconfig.debug > +++ b/arch/x86/Kconfig.debug > @@ -5,23 +5,6 @@ config TRACE_IRQFLAGS_SUPPORT > > source "lib/Kconfig.debug" > > -config STRICT_DEVMEM > - bool "Filter access to /dev/mem" > - ---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. > - > config X86_VERBOSE_BOOTUP > bool "Enable verbose x86 bootup info messages" > default y > diff --git a/drivers/char/Kconfig b/drivers/char/Kconfig > index efefd12..39f7817 100644 > --- a/drivers/char/Kconfig > +++ b/drivers/char/Kconfig > @@ -6,6 +6,22 @@ menu "Character devices" > > source "drivers/tty/Kconfig" > > +config STRICT_DEVMEM > + bool "Reduced access to /dev/mem" > + depends on HAVE_ARCH_RESTRICTED_DEVMEM > + default y > + 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. > + > + If this option is switched on, the /dev/mem file restricts userspace > + access to an architecture-specific subset of the physical address > + space. Great consolidation, thanks! I would probably expand this help text a bit to include some of details mentioned in the x86 portion of the option. For example: If this option is switched on, the /dev/mem file restricts userspace access to an architecture-specific subset of the physical address space. For example on x86, PCI space and BIOS code and data regions. This is sufficient for things like dosemu and non-KMS Xorg and all common users of /dev/mem. Thanks! -Kees > + > + If in doubt, say Y. > + > config DEVKMEM > bool "/dev/kmem virtual device support" > default y > -- > 1.7.10.4 > -- Kees Cook Chrome OS Security -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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