From 591b1d8d86074ac3a3163d89bcfe7b232cf83902 Mon Sep 17 00:00:00 2001 From: Dave Hansen Date: Mon, 14 Dec 2015 11:06:34 -0800 Subject: x86/mm/pkeys: Add missing Documentation Stefan Richter noticed that the X86_INTEL_MEMORY_PROTECTION_KEYS option in arch/x86/Kconfig references Documentation/x86/protection-keys.txt, but the file does not exist. This is a patch merging mishap: the final (v8) version of the pkeys series did not include the documentation patch 32 and v7 included. Add it now. Reported-by: Stefan Richter Signed-off-by: Dave Hansen Cc: Andy Lutomirski Cc: Borislav Petkov Cc: Brian Gerst Cc: Dave Hansen Cc: Denys Vlasenko Cc: H. Peter Anvin Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: linux-mm@kvack.org Link: http://lkml.kernel.org/r/20151214190634.426BEE41@viggo.jf.intel.com [ Added changelog. ] Signed-off-by: Ingo Molnar Signed-off-by: Ingo Molnar diff --git a/Documentation/x86/protection-keys.txt b/Documentation/x86/protection-keys.txt new file mode 100644 index 0000000..c281ded --- /dev/null +++ b/Documentation/x86/protection-keys.txt @@ -0,0 +1,27 @@ +Memory Protection Keys for Userspace (PKU aka PKEYs) is a CPU feature +which will be found on future Intel CPUs. + +Memory Protection Keys provides a mechanism for enforcing page-based +protections, but without requiring modification of the page tables +when an application changes protection domains. It works by +dedicating 4 previously ignored bits in each page table entry to a +"protection key", giving 16 possible keys. + +There is also a new user-accessible register (PKRU) with two separate +bits (Access Disable and Write Disable) for each key. Being a CPU +register, PKRU is inherently thread-local, potentially giving each +thread a different set of protections from every other thread. + +There are two new instructions (RDPKRU/WRPKRU) for reading and writing +to the new register. The feature is only available in 64-bit mode, +even though there is theoretically space in the PAE PTEs. These +permissions are enforced on data access only and have no effect on +instruction fetches. + +=========================== Config Option =========================== + +This config option adds approximately 1.5kb of text. and 50 bytes of +data to the executable. A workload which does large O_DIRECT reads +of holes in XFS files was run to exercise get_user_pages_fast(). No +performance delta was observed with the config option +enabled or disabled. -- cgit v0.10.2 From 6d92bc9d483aa1751755a66fee8fb39dffb088c0 Mon Sep 17 00:00:00 2001 From: "H.J. Lu" Date: Wed, 16 Mar 2016 20:04:35 -0700 Subject: x86/build: Build compressed x86 kernels as PIE The 32-bit x86 assembler in binutils 2.26 will generate R_386_GOT32X relocation to get the symbol address in PIC. When the compressed x86 kernel isn't built as PIC, the linker optimizes R_386_GOT32X relocations to their fixed symbol addresses. However, when the compressed x86 kernel is loaded at a different address, it leads to the following load failure: Failed to allocate space for phdrs during the decompression stage. If the compressed x86 kernel is relocatable at run-time, it should be compiled with -fPIE, instead of -fPIC, if possible and should be built as Position Independent Executable (PIE) so that linker won't optimize R_386_GOT32X relocation to its fixed symbol address. Older linkers generate R_386_32 relocations against locally defined symbols, _bss, _ebss, _got and _egot, in PIE. It isn't wrong, just less optimal than R_386_RELATIVE. But the x86 kernel fails to properly handle R_386_32 relocations when relocating the kernel. To generate R_386_RELATIVE relocations, we mark _bss, _ebss, _got and _egot as hidden in both 32-bit and 64-bit x86 kernels. To build a 64-bit compressed x86 kernel as PIE, we need to disable the relocation overflow check to avoid relocation overflow errors. We do this with a new linker command-line option, -z noreloc-overflow, which got added recently: commit 4c10bbaa0912742322f10d9d5bb630ba4e15dfa7 Author: H.J. Lu Date: Tue Mar 15 11:07:06 2016 -0700 Add -z noreloc-overflow option to x86-64 ld Add -z noreloc-overflow command-line option to the x86-64 ELF linker to disable relocation overflow check. This can be used to avoid relocation overflow check if there will be no dynamic relocation overflow at run-time. The 64-bit compressed x86 kernel is built as PIE only if the linker supports -z noreloc-overflow. So far 64-bit relocatable compressed x86 kernel boots fine even when it is built as a normal executable. Signed-off-by: H.J. Lu Cc: Andy Lutomirski Cc: Borislav Petkov Cc: Brian Gerst Cc: Denys Vlasenko Cc: H. Peter Anvin Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: linux-kernel@vger.kernel.org [ Edited the changelog and comments. ] Signed-off-by: Ingo Molnar diff --git a/arch/x86/boot/compressed/Makefile b/arch/x86/boot/compressed/Makefile index 6915ff2..8774cb2 100644 --- a/arch/x86/boot/compressed/Makefile +++ b/arch/x86/boot/compressed/Makefile @@ -26,7 +26,7 @@ targets := vmlinux vmlinux.bin vmlinux.bin.gz vmlinux.bin.bz2 vmlinux.bin.lzma \ vmlinux.bin.xz vmlinux.bin.lzo vmlinux.bin.lz4 KBUILD_CFLAGS := -m$(BITS) -D__KERNEL__ $(LINUX_INCLUDE) -O2 -KBUILD_CFLAGS += -fno-strict-aliasing -fPIC +KBUILD_CFLAGS += -fno-strict-aliasing $(call cc-option, -fPIE, -fPIC) KBUILD_CFLAGS += -DDISABLE_BRANCH_PROFILING cflags-$(CONFIG_X86_32) := -march=i386 cflags-$(CONFIG_X86_64) := -mcmodel=small @@ -40,6 +40,18 @@ GCOV_PROFILE := n UBSAN_SANITIZE :=n LDFLAGS := -m elf_$(UTS_MACHINE) +ifeq ($(CONFIG_RELOCATABLE),y) +# If kernel is relocatable, build compressed kernel as PIE. +ifeq ($(CONFIG_X86_32),y) +LDFLAGS += $(call ld-option, -pie) $(call ld-option, --no-dynamic-linker) +else +# To build 64-bit compressed kernel as PIE, we disable relocation +# overflow check to avoid relocation overflow error with a new linker +# command-line option, -z noreloc-overflow. +LDFLAGS += $(shell $(LD) --help 2>&1 | grep -q "\-z noreloc-overflow" \ + && echo "-z noreloc-overflow -pie --no-dynamic-linker") +endif +endif LDFLAGS_vmlinux := -T hostprogs-y := mkpiggy diff --git a/arch/x86/boot/compressed/head_32.S b/arch/x86/boot/compressed/head_32.S index 8ef964d..0256064 100644 --- a/arch/x86/boot/compressed/head_32.S +++ b/arch/x86/boot/compressed/head_32.S @@ -31,6 +31,34 @@ #include #include +/* + * The 32-bit x86 assembler in binutils 2.26 will generate R_386_GOT32X + * relocation to get the symbol address in PIC. When the compressed x86 + * kernel isn't built as PIC, the linker optimizes R_386_GOT32X + * relocations to their fixed symbol addresses. However, when the + * compressed x86 kernel is loaded at a different address, it leads + * to the following load failure: + * + * Failed to allocate space for phdrs + * + * during the decompression stage. + * + * If the compressed x86 kernel is relocatable at run-time, it should be + * compiled with -fPIE, instead of -fPIC, if possible and should be built as + * Position Independent Executable (PIE) so that linker won't optimize + * R_386_GOT32X relocation to its fixed symbol address. Older + * linkers generate R_386_32 relocations against locally defined symbols, + * _bss, _ebss, _got and _egot, in PIE. It isn't wrong, just less + * optimal than R_386_RELATIVE. But the x86 kernel fails to properly handle + * R_386_32 relocations when relocating the kernel. To generate + * R_386_RELATIVE relocations, we mark _bss, _ebss, _got and _egot as + * hidden: + */ + .hidden _bss + .hidden _ebss + .hidden _got + .hidden _egot + __HEAD ENTRY(startup_32) #ifdef CONFIG_EFI_STUB diff --git a/arch/x86/boot/compressed/head_64.S b/arch/x86/boot/compressed/head_64.S index b0c0d16..86558a1 100644 --- a/arch/x86/boot/compressed/head_64.S +++ b/arch/x86/boot/compressed/head_64.S @@ -33,6 +33,14 @@ #include #include +/* + * Locally defined symbols should be marked hidden: + */ + .hidden _bss + .hidden _ebss + .hidden _got + .hidden _egot + __HEAD .code32 ENTRY(startup_32) -- cgit v0.10.2 From f87e0434a3bedeb5e4d75d96d9f3ad424dae6b33 Mon Sep 17 00:00:00 2001 From: Rusty Russell Date: Fri, 1 Apr 2016 12:15:46 +1030 Subject: lguest, x86/entry/32: Fix handling of guest syscalls using interrupt gates In a798f091113e ("x86/entry/32: Change INT80 to be an interrupt gate") Andy broke lguest. This is because lguest had special code to allow the 0x80 trap gate go straight into the guest itself; interrupts gates (without more work, as mentioned in the file's comments) bounce via the hypervisor. His change made them go via the hypervisor, but as it's in the range of normal hardware interrupts, they were not directed through to the guest at all. Turns out the guest userspace isn't very effective if syscalls are all noops. I haven't ripped out all the now-useless trap-direct-to-guest-kernel code yet, since it will still be needed if someone decides to update this optimization. Signed-off-by: Rusty Russell Cc: Andy Lutomirski Cc: Andy Lutomirski Cc: Borislav Petkov Cc: Brian Gerst Cc: Denys Vlasenko Cc: H. Peter Anvin Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: Weisbecker Cc: x86\@kernel.org Link: http://lkml.kernel.org/r/87fuv685kl.fsf@rustcorp.com.au Signed-off-by: Ingo Molnar diff --git a/drivers/lguest/interrupts_and_traps.c b/drivers/lguest/interrupts_and_traps.c index eb934b0..67392b6 100644 --- a/drivers/lguest/interrupts_and_traps.c +++ b/drivers/lguest/interrupts_and_traps.c @@ -331,7 +331,7 @@ void set_interrupt(struct lg_cpu *cpu, unsigned int irq) * Actually now I think of it, it's possible that Ron *is* half the Plan 9 * userbase. Oh well. */ -static bool could_be_syscall(unsigned int num) +bool could_be_syscall(unsigned int num) { /* Normal Linux IA32_SYSCALL_VECTOR or reserved vector? */ return num == IA32_SYSCALL_VECTOR || num == syscall_vector; @@ -416,6 +416,10 @@ bool deliver_trap(struct lg_cpu *cpu, unsigned int num) * * This routine indicates if a particular trap number could be delivered * directly. + * + * Unfortunately, Linux 4.6 started using an interrupt gate instead of a + * trap gate for syscalls, so this trick is ineffective. See Mastery for + * how we could do this anyway... */ static bool direct_trap(unsigned int num) { diff --git a/drivers/lguest/lg.h b/drivers/lguest/lg.h index ac8ad04..69b3814 100644 --- a/drivers/lguest/lg.h +++ b/drivers/lguest/lg.h @@ -167,6 +167,7 @@ void guest_set_clockevent(struct lg_cpu *cpu, unsigned long delta); bool send_notify_to_eventfd(struct lg_cpu *cpu); void init_clockdev(struct lg_cpu *cpu); bool check_syscall_vector(struct lguest *lg); +bool could_be_syscall(unsigned int num); int init_interrupts(void); void free_interrupts(void); diff --git a/drivers/lguest/x86/core.c b/drivers/lguest/x86/core.c index 6a4cd77..adc162c 100644 --- a/drivers/lguest/x86/core.c +++ b/drivers/lguest/x86/core.c @@ -429,8 +429,12 @@ void lguest_arch_handle_trap(struct lg_cpu *cpu) return; break; case 32 ... 255: + /* This might be a syscall. */ + if (could_be_syscall(cpu->regs->trapnum)) + break; + /* - * These values mean a real interrupt occurred, in which case + * Other values mean a real interrupt occurred, in which case * the Host handler has already been run. We just do a * friendly check if another process should now be run, then * return to run the Guest again. -- cgit v0.10.2 From a3125494cff084b098c80bb36fbe2061ffed9d52 Mon Sep 17 00:00:00 2001 From: Tony Luck Date: Wed, 6 Apr 2016 10:05:16 +0200 Subject: x86/mce: Avoid using object after free in genpool When we loop over all queued machine check error records to pass them to the registered notifiers we use llist_for_each_entry(). But the loop calls gen_pool_free() for the entry in the body of the loop - and then the iterator looks at node->next after the free. Use llist_for_each_entry_safe() instead. Signed-off-by: Tony Luck Signed-off-by: Borislav Petkov Cc: Cc: Gong Chen Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: linux-edac Link: http://lkml.kernel.org/r/0205920@agluck-desk.sc.intel.com Link: http://lkml.kernel.org/r/1459929916-12852-4-git-send-email-bp@alien8.de Signed-off-by: Ingo Molnar diff --git a/arch/x86/kernel/cpu/mcheck/mce-genpool.c b/arch/x86/kernel/cpu/mcheck/mce-genpool.c index 0a85010..2658e2a 100644 --- a/arch/x86/kernel/cpu/mcheck/mce-genpool.c +++ b/arch/x86/kernel/cpu/mcheck/mce-genpool.c @@ -29,7 +29,7 @@ static char gen_pool_buf[MCE_POOLSZ]; void mce_gen_pool_process(void) { struct llist_node *head; - struct mce_evt_llist *node; + struct mce_evt_llist *node, *tmp; struct mce *mce; head = llist_del_all(&mce_event_llist); @@ -37,7 +37,7 @@ void mce_gen_pool_process(void) return; head = llist_reverse_order(head); - llist_for_each_entry(node, head, llnode) { + llist_for_each_entry_safe(node, tmp, head, llnode) { mce = &node->mce; atomic_notifier_call_chain(&x86_mce_decoder_chain, 0, mce); gen_pool_free(mce_evt_pool, (unsigned long)node, sizeof(*node)); -- cgit v0.10.2