From 6f6a7c09c4065a5b140194dfcfe4cf7104fec4d2 Mon Sep 17 00:00:00 2001 From: Thomas Gleixner Date: Thu, 21 Oct 2021 15:55:08 -0700 Subject: [PATCH] x86/fpu: Add members to struct fpu to cache permission information Dynamically enabled features can be requested by any thread of a running process at any time. The request does neither enable the feature nor allocate larger buffers. It just stores the permission to use the feature by adding the features to the permission bitmap and by calculating the required sizes for kernel and user space. The reallocation of the kernel buffer happens when the feature is used for the first time which is caught by an exception. The permission bitmap is then checked and if the feature is permitted, then it becomes fully enabled. If not, the task dies similarly to a task which uses an undefined instruction. The size information is precomputed to allow proper sigaltstack size checks once the feature is permitted, but not yet in use because otherwise this would open race windows where too small stacks could be installed causing a later fail on signal delivery. Initialize them to the default feature set and sizes. Signed-off-by: Thomas Gleixner Signed-off-by: Chang S. Bae Signed-off-by: Borislav Petkov Link: https://lkml.kernel.org/r/20211021225527.10184-5-chang.seok.bae@intel.com --- arch/x86/include/asm/fpu/types.h | 46 ++++++++++++++++++++++++++++++++++++++++ arch/x86/kernel/fpu/core.c | 5 +++++ 2 files changed, 51 insertions(+) diff --git a/arch/x86/include/asm/fpu/types.h b/arch/x86/include/asm/fpu/types.h index c72cb2269adc..c3ec56279767 100644 --- a/arch/x86/include/asm/fpu/types.h +++ b/arch/x86/include/asm/fpu/types.h @@ -352,6 +352,45 @@ struct fpstate { /* @regs is dynamically sized! Don't add anything after @regs! */ } __aligned(64); +struct fpu_state_perm { + /* + * @__state_perm: + * + * This bitmap indicates the permission for state components, which + * are available to a thread group. The permission prctl() sets the + * enabled state bits in thread_group_leader()->thread.fpu. + * + * All run time operations use the per thread information in the + * currently active fpu.fpstate which contains the xfeature masks + * and sizes for kernel and user space. + * + * This master permission field is only to be used when + * task.fpu.fpstate based checks fail to validate whether the task + * is allowed to expand it's xfeatures set which requires to + * allocate a larger sized fpstate buffer. + * + * Do not access this field directly. Use the provided helper + * function. Unlocked access is possible for quick checks. + */ + u64 __state_perm; + + /* + * @__state_size: + * + * The size required for @__state_perm. Only valid to access + * with sighand locked. + */ + unsigned int __state_size; + + /* + * @__user_state_size: + * + * The size required for @__state_perm user part. Only valid to + * access with sighand locked. + */ + unsigned int __user_state_size; +}; + /* * Highest level per task FPU state data structure that * contains the FPU register state plus various FPU @@ -396,6 +435,13 @@ struct fpu { struct fpstate *__task_fpstate; /* + * @perm: + * + * Permission related information + */ + struct fpu_state_perm perm; + + /* * @__fpstate: * * Initial in-memory storage for FPU registers which are saved in diff --git a/arch/x86/kernel/fpu/core.c b/arch/x86/kernel/fpu/core.c index 9c475e2efd4d..b05f6a3b2057 100644 --- a/arch/x86/kernel/fpu/core.c +++ b/arch/x86/kernel/fpu/core.c @@ -412,6 +412,11 @@ void fpstate_reset(struct fpu *fpu) /* Set the fpstate pointer to the default fpstate */ fpu->fpstate = &fpu->__fpstate; __fpstate_reset(fpu->fpstate); + + /* Initialize the permission related info in fpu */ + fpu->perm.__state_perm = fpu_kernel_cfg.default_features; + fpu->perm.__state_size = fpu_kernel_cfg.default_size; + fpu->perm.__user_state_size = fpu_user_cfg.default_size; } /* Clone current's FPU state on fork */ -- 2.11.0