From d892454b6814f07da676dae5e686cf221d34a1af Mon Sep 17 00:00:00 2001 From: Dave Hansen Date: Wed, 30 Jun 2021 18:57:03 -0700 Subject: [PATCH] selftests/vm/pkeys: exercise x86 XSAVE init state On x86, there is a set of instructions used to save and restore register state collectively known as the XSAVE architecture. There are about a dozen different features managed with XSAVE. The protection keys register, PKRU, is one of those features. The hardware optimizes XSAVE by tracking when the state has not changed from its initial (init) state. In this case, it can avoid the cost of writing state to memory (it would usually just be a bunch of 0's). When the pkey register is 0x0 the hardware optionally choose to track the register as being in the init state (optimize away the writes). AMD CPUs do this more aggressively compared to Intel. On x86, PKRU is rarely in its (very permissive) init state. Instead, the value defaults to something very restrictive. It is not surprising that bugs have popped up in the rare cases when PKRU reaches its init state. Add a protection key selftest which gets the protection keys register into its init state in a way that should work on Intel and AMD. Then, do a bunch of pkey register reads to watch for inadvertent changes. This adds "-mxsave" to CFLAGS for all the x86 vm selftests in order to allow use of the XSAVE instruction __builtin functions. This will make the builtins available on all of the vm selftests, but is expected to be harmless. Link: https://lkml.kernel.org/r/20210611164202.1849B712@viggo.jf.intel.com Signed-off-by: Dave Hansen Signed-off-by: Thomas Gleixner Tested-by: Aneesh Kumar K.V Cc: Ram Pai Cc: Sandipan Das Cc: Florian Weimer Cc: "Desnes A. Nunes do Rosario" Cc: Ingo Molnar Cc: Thiago Jung Bauermann Cc: Michael Ellerman Cc: Michal Hocko Cc: Michal Suchanek Cc: Shuah Khan Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- tools/testing/selftests/vm/Makefile | 4 +- tools/testing/selftests/vm/pkey-x86.h | 1 + tools/testing/selftests/vm/protection_keys.c | 73 ++++++++++++++++++++ 3 files changed, 76 insertions(+), 2 deletions(-) diff --git a/tools/testing/selftests/vm/Makefile b/tools/testing/selftests/vm/Makefile index 8be00319beca..812bc03e3142 100644 --- a/tools/testing/selftests/vm/Makefile +++ b/tools/testing/selftests/vm/Makefile @@ -101,7 +101,7 @@ $(1) $(1)_64: $(OUTPUT)/$(1)_64 endef ifeq ($(CAN_BUILD_I386),1) -$(BINARIES_32): CFLAGS += -m32 +$(BINARIES_32): CFLAGS += -m32 -mxsave $(BINARIES_32): LDLIBS += -lrt -ldl -lm $(BINARIES_32): $(OUTPUT)/%_32: %.c $(CC) $(CFLAGS) $(EXTRA_CFLAGS) $(notdir $^) $(LDLIBS) -o $@ @@ -109,7 +109,7 @@ $(foreach t,$(TARGETS),$(eval $(call gen-target-rule-32,$(t)))) endif ifeq ($(CAN_BUILD_X86_64),1) -$(BINARIES_64): CFLAGS += -m64 +$(BINARIES_64): CFLAGS += -m64 -mxsave $(BINARIES_64): LDLIBS += -lrt -ldl $(BINARIES_64): $(OUTPUT)/%_64: %.c $(CC) $(CFLAGS) $(EXTRA_CFLAGS) $(notdir $^) $(LDLIBS) -o $@ diff --git a/tools/testing/selftests/vm/pkey-x86.h b/tools/testing/selftests/vm/pkey-x86.h index 3be20f5d5275..e4a4ce2b826d 100644 --- a/tools/testing/selftests/vm/pkey-x86.h +++ b/tools/testing/selftests/vm/pkey-x86.h @@ -126,6 +126,7 @@ static inline u32 pkey_bit_position(int pkey) #define XSTATE_PKEY_BIT (9) #define XSTATE_PKEY 0x200 +#define XSTATE_BV_OFFSET 512 int pkey_reg_xstate_offset(void) { diff --git a/tools/testing/selftests/vm/protection_keys.c b/tools/testing/selftests/vm/protection_keys.c index 87eecd5ba577..2d0ae88665db 100644 --- a/tools/testing/selftests/vm/protection_keys.c +++ b/tools/testing/selftests/vm/protection_keys.c @@ -1277,6 +1277,78 @@ void test_pkey_alloc_exhaust(int *ptr, u16 pkey) } } +void arch_force_pkey_reg_init(void) +{ +#if defined(__i386__) || defined(__x86_64__) /* arch */ + u64 *buf; + + /* + * All keys should be allocated and set to allow reads and + * writes, so the register should be all 0. If not, just + * skip the test. + */ + if (read_pkey_reg()) + return; + + /* + * Just allocate an absurd about of memory rather than + * doing the XSAVE size enumeration dance. + */ + buf = mmap(NULL, 1*MB, PROT_READ|PROT_WRITE, MAP_ANONYMOUS|MAP_PRIVATE, -1, 0); + + /* These __builtins require compiling with -mxsave */ + + /* XSAVE to build a valid buffer: */ + __builtin_ia32_xsave(buf, XSTATE_PKEY); + /* Clear XSTATE_BV[PKRU]: */ + buf[XSTATE_BV_OFFSET/sizeof(u64)] &= ~XSTATE_PKEY; + /* XRSTOR will likely get PKRU back to the init state: */ + __builtin_ia32_xrstor(buf, XSTATE_PKEY); + + munmap(buf, 1*MB); +#endif +} + + +/* + * This is mostly useless on ppc for now. But it will not + * hurt anything and should give some better coverage as + * a long-running test that continually checks the pkey + * register. + */ +void test_pkey_init_state(int *ptr, u16 pkey) +{ + int err; + int allocated_pkeys[NR_PKEYS] = {0}; + int nr_allocated_pkeys = 0; + int i; + + for (i = 0; i < NR_PKEYS; i++) { + int new_pkey = alloc_pkey(); + + if (new_pkey < 0) + continue; + allocated_pkeys[nr_allocated_pkeys++] = new_pkey; + } + + dprintf3("%s()::%d\n", __func__, __LINE__); + + arch_force_pkey_reg_init(); + + /* + * Loop for a bit, hoping to get exercise the kernel + * context switch code. + */ + for (i = 0; i < 1000000; i++) + read_pkey_reg(); + + for (i = 0; i < nr_allocated_pkeys; i++) { + err = sys_pkey_free(allocated_pkeys[i]); + pkey_assert(!err); + read_pkey_reg(); /* for shadow checking */ + } +} + /* * pkey 0 is special. It is allocated by default, so you do not * have to call pkey_alloc() to use it first. Make sure that it @@ -1508,6 +1580,7 @@ void (*pkey_tests[])(int *ptr, u16 pkey) = { test_implicit_mprotect_exec_only_memory, test_mprotect_with_pkey_0, test_ptrace_of_child, + test_pkey_init_state, test_pkey_syscalls_on_non_allocated_pkey, test_pkey_syscalls_bad_args, test_pkey_alloc_exhaust,