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authorChang S. Bae <chang.seok.bae@intel.com>2021-10-21 15:55:10 -0700
committerBorislav Petkov <bp@suse.de>2021-10-26 10:18:09 +0200
commitdb8268df0983adc2bb1fb48c9e5f7bfbb5f617f3 (patch)
treef17ecc439425dc523f67659302edc19d2ab839d7 /arch/x86/include/uapi
parentc33f0a81a2cf3920465309ce683534751bb86485 (diff)
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x86/arch_prctl: Add controls for dynamic XSTATE components
Dynamically enabled XSTATE features are by default disabled for all processes. A process has to request permission to use such a feature. To support this implement a architecture specific prctl() with the options: - ARCH_GET_XCOMP_SUPP Copies the supported feature bitmap into the user space provided u64 storage. The pointer is handed in via arg2 - ARCH_GET_XCOMP_PERM Copies the process wide permitted feature bitmap into the user space provided u64 storage. The pointer is handed in via arg2 - ARCH_REQ_XCOMP_PERM Request permission for a feature set. A feature set can be mapped to a facility, e.g. AMX, and can require one or more XSTATE components to be enabled. The feature argument is the number of the highest XSTATE component which is required for a facility to work. The request argument is not a user supplied bitmap because that makes filtering harder (think seccomp) and even impossible because to support 32bit tasks the argument would have to be a pointer. The permission mechanism works this way: Task asks for permission for a facility and kernel checks whether that's supported. If supported it does: 1) Check whether permission has already been granted 2) Compute the size of the required kernel and user space buffer (sigframe) size. 3) Validate that no task has a sigaltstack installed which is smaller than the resulting sigframe size 4) Add the requested feature bit(s) to the permission bitmap of current->group_leader->fpu and store the sizes in the group leaders fpu struct as well. If that is successful then the feature is still not enabled for any of the tasks. The first usage of a related instruction will result in a #NM trap. The trap handler validates the permission bit of the tasks group leader and if permitted it installs a larger kernel buffer and transfers the permission and size info to the new fpstate container which makes all the FPU functions which require per task information aware of the extended feature set. [ tglx: Adopted to new base code, added missing serialization, massaged namings, comments and changelog ] Signed-off-by: Chang S. Bae <chang.seok.bae@intel.com> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Signed-off-by: Chang S. Bae <chang.seok.bae@intel.com> Signed-off-by: Borislav Petkov <bp@suse.de> Link: https://lkml.kernel.org/r/20211021225527.10184-7-chang.seok.bae@intel.com
Diffstat (limited to 'arch/x86/include/uapi')
-rw-r--r--arch/x86/include/uapi/asm/prctl.h4
1 files changed, 4 insertions, 0 deletions
diff --git a/arch/x86/include/uapi/asm/prctl.h b/arch/x86/include/uapi/asm/prctl.h
index 5a6aac9fa41f..754a07856817 100644
--- a/arch/x86/include/uapi/asm/prctl.h
+++ b/arch/x86/include/uapi/asm/prctl.h
@@ -10,6 +10,10 @@
#define ARCH_GET_CPUID 0x1011
#define ARCH_SET_CPUID 0x1012
+#define ARCH_GET_XCOMP_SUPP 0x1021
+#define ARCH_GET_XCOMP_PERM 0x1022
+#define ARCH_REQ_XCOMP_PERM 0x1023
+
#define ARCH_MAP_VDSO_X32 0x2001
#define ARCH_MAP_VDSO_32 0x2002
#define ARCH_MAP_VDSO_64 0x2003