From: Rik van Riel <r...@redhat.com> On Skylake CPUs I noticed that XRSTOR is unable to deal with states created by copyout_from_xsaves() if the xstate has only SSE/YMM state, and no FP state. That is, xfeatures had XFEATURE_MASK_SSE set, but not XFEATURE_MASK_FP.
The reason is that part of the SSE/YMM state lives in the MXCSR and MXCSR_FLAGS fields of the FP state. Ensure that whenever we copy SSE or YMM state around, the MXCSR and MXCSR_FLAGS fields are also copied around. Signed-off-by: Rik van Riel <r...@redhat.com> Cc: Andy Lutomirski <l...@kernel.org> Cc: Borislav Petkov <b...@alien8.de> Cc: Borislav Petkov <b...@suse.de> Cc: Dave Hansen <dave.han...@linux.intel.com> Cc: Fenghua Yu <fenghua...@intel.com> Cc: H. Peter Anvin <h...@zytor.com> Cc: Linus Torvalds <torva...@linux-foundation.org> Cc: Oleg Nesterov <o...@redhat.com> Cc: Peter Zijlstra <pet...@infradead.org> Cc: Thomas Gleixner <t...@linutronix.de> Cc: Yu-cheng Yu <yu-cheng...@intel.com> Link: http://lkml.kernel.org/r/20170210085445.0f1cc...@annuminas.surriel.com Signed-off-by: Ingo Molnar <mi...@kernel.org> --- arch/x86/include/asm/fpu/types.h | 3 +++ arch/x86/kernel/fpu/xstate.c | 42 ++++++++++++++++++++++++++++++++++++++++++ 2 files changed, 45 insertions(+) diff --git a/arch/x86/include/asm/fpu/types.h b/arch/x86/include/asm/fpu/types.h index 0c314a397cf5..71db45ca8870 100644 --- a/arch/x86/include/asm/fpu/types.h +++ b/arch/x86/include/asm/fpu/types.h @@ -68,6 +68,9 @@ struct fxregs_state { /* Default value for fxregs_state.mxcsr: */ #define MXCSR_DEFAULT 0x1f80 +/* Copy both mxcsr & mxcsr_flags with a single u64 memcpy: */ +#define MXCSR_AND_FLAGS_SIZE sizeof(u64) + /* * Software based FPU emulation state. This is arbitrary really, * it matches the x87 format to make it easier to understand: diff --git a/arch/x86/kernel/fpu/xstate.c b/arch/x86/kernel/fpu/xstate.c index 0ef35040d0ad..41c52256bdce 100644 --- a/arch/x86/kernel/fpu/xstate.c +++ b/arch/x86/kernel/fpu/xstate.c @@ -921,6 +921,23 @@ int arch_set_user_pkey_access(struct task_struct *tsk, int pkey, #endif /* ! CONFIG_ARCH_HAS_PKEYS */ /* + * Weird legacy quirk: SSE and YMM states store information in the + * MXCSR and MXCSR_FLAGS fields of the FP area. That means if the FP + * area is marked as unused in the xfeatures header, we need to copy + * MXCSR and MXCSR_FLAGS if either SSE or YMM are in use. + */ +static inline bool xfeatures_mxcsr_quirk(u64 xfeatures) +{ + if (!(xfeatures & (XFEATURE_MASK_SSE|XFEATURE_MASK_YMM))) + return 0; + + if (xfeatures & XFEATURE_MASK_FP) + return 0; + + return 1; +} + +/* * This is similar to user_regset_copyout(), but will not add offset to * the source data pointer or increment pos, count, kbuf, and ubuf. */ @@ -988,6 +1005,12 @@ int copy_xstate_to_kernel(void *kbuf, struct xregs_state *xsave, unsigned int of } + if (xfeatures_mxcsr_quirk(header.xfeatures)) { + offset = offsetof(struct fxregs_state, mxcsr); + size = MXCSR_AND_FLAGS_SIZE; + __copy_xstate_to_kernel(kbuf, &xsave->i387.mxcsr, offset, size, size_total); + } + /* * Fill xsave->i387.sw_reserved value for ptrace frame: */ @@ -1070,6 +1093,12 @@ int copy_xstate_to_user(void __user *ubuf, struct xregs_state *xsave, unsigned i } + if (xfeatures_mxcsr_quirk(header.xfeatures)) { + offset = offsetof(struct fxregs_state, mxcsr); + size = MXCSR_AND_FLAGS_SIZE; + __copy_xstate_to_user(ubuf, &xsave->i387.mxcsr, offset, size, size_total); + } + /* * Fill xsave->i387.sw_reserved value for ptrace frame: */ @@ -1122,6 +1151,12 @@ int copy_kernel_to_xstate(struct xregs_state *xsave, const void *kbuf) } } + if (xfeatures_mxcsr_quirk(xfeatures)) { + offset = offsetof(struct fxregs_state, mxcsr); + size = MXCSR_AND_FLAGS_SIZE; + memcpy(&xsave->i387.mxcsr, kbuf + offset, size); + } + /* * The state that came in from userspace was user-state only. * Mask all the user states out of 'xfeatures': @@ -1177,6 +1212,13 @@ int copy_user_to_xstate(struct xregs_state *xsave, const void __user *ubuf) } } + if (xfeatures_mxcsr_quirk(xfeatures)) { + offset = offsetof(struct fxregs_state, mxcsr); + size = MXCSR_AND_FLAGS_SIZE; + if (__copy_from_user(&xsave->i387.mxcsr, ubuf + offset, size)) + return -EFAULT; + } + /* * The state that came in from userspace was user-state only. * Mask all the user states out of 'xfeatures': -- 2.11.0
