| Message ID | 20180921150351.20898-27-yu-cheng.yu@intel.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | Control Flow Enforcement: Shadow Stack | expand |
On Fri, Sep 21, 2018 at 08:03:50AM -0700, Yu-cheng Yu wrote: > arch_prctl(ARCH_CET_STATUS, unsigned long *addr) > Return CET feature status. > > The parameter 'addr' is a pointer to a user buffer. > On returning to the caller, the kernel fills the following > information: > > *addr = SHSTK/IBT status > *(addr + 1) = SHSTK base address > *(addr + 2) = SHSTK size The subtle detail here is that x32 binaries will get 64-bit value, which is not entirely obvious. I think, it might be better to define a structure type for it as a part of UAPI, for example: struct user_cet_status { __u32 struct_size; __u32 features; __kernel_ulong_t shstk_base; __kernel_ulong_t shstk_size; }; Adding "struct_size" field along with appropriate checks will also allow for possible extensions, if they ever appear. > arch_prctl(ARCH_CET_DISABLE, unsigned long features) > Disable CET features specified in 'features'. Return > -EPERM if CET is locked. While x86_64 and x32 will have 64-bit space for feature bits, IA-32 will have only 32 bits. > arch_prctl(ARCH_CET_LOCK) > Lock in CET feature. > > arch_prctl(ARCH_CET_ALLOC_SHSTK, unsigned long *addr) > Allocate a new SHSTK. > > The parameter 'addr' is a pointer to a user buffer and indicates > the desired SHSTK size to allocate. On returning to the caller > the buffer contains the address of the new SHSTK. Again, on x32 that will be a pointer to a 64-bit value, which is not entirely obvious from this description. It's not clear whether inability to enable some CET feature in runtime is unavailable by design or by omission; same for setting (an allocated) shadow stack as task's shadow stack. > > Signed-off-by: H.J. Lu <hjl.tools@gmail.com> > Signed-off-by: Yu-cheng Yu <yu-cheng.yu@intel.com> > --- > arch/x86/include/asm/cet.h | 5 ++ > arch/x86/include/uapi/asm/prctl.h | 5 ++ > arch/x86/kernel/Makefile | 2 +- > arch/x86/kernel/cet.c | 27 +++++++++++ > arch/x86/kernel/cet_prctl.c | 79 +++++++++++++++++++++++++++++++ > arch/x86/kernel/process.c | 5 ++ > 6 files changed, 122 insertions(+), 1 deletion(-) > create mode 100644 arch/x86/kernel/cet_prctl.c > > diff --git a/arch/x86/include/asm/cet.h b/arch/x86/include/asm/cet.h > index b7b33e1026bb..212bd68e31d3 100644 > --- a/arch/x86/include/asm/cet.h > +++ b/arch/x86/include/asm/cet.h > @@ -12,19 +12,24 @@ struct task_struct; > struct cet_status { > unsigned long shstk_base; > unsigned long shstk_size; > + unsigned int locked:1; > unsigned int shstk_enabled:1; > }; > > #ifdef CONFIG_X86_INTEL_CET > +int prctl_cet(int option, unsigned long arg2); > int cet_setup_shstk(void); > int cet_setup_thread_shstk(struct task_struct *p); > +int cet_alloc_shstk(unsigned long *arg); > void cet_disable_shstk(void); > void cet_disable_free_shstk(struct task_struct *p); > int cet_restore_signal(unsigned long ssp); > int cet_setup_signal(bool ia32, unsigned long rstor, unsigned long *new_ssp); > #else > +static inline int prctl_cet(int option, unsigned long arg2) { return 0; } Why 0 and not -EINVAL? > static inline int cet_setup_shstk(void) { return 0; } 0 here also looks strange. > static inline int cet_setup_thread_shstk(struct task_struct *p) { return 0; } And here. > +static inline int cet_alloc_shstk(unsigned long *arg) { return -EINVAL; } > static inline void cet_disable_shstk(void) {} > static inline void cet_disable_free_shstk(struct task_struct *p) {} > static inline int cet_restore_signal(unsigned long ssp) { return 0; } > diff --git a/arch/x86/include/uapi/asm/prctl.h b/arch/x86/include/uapi/asm/prctl.h > index 5a6aac9fa41f..3aec1088e01d 100644 > --- a/arch/x86/include/uapi/asm/prctl.h > +++ b/arch/x86/include/uapi/asm/prctl.h > @@ -14,4 +14,9 @@ > #define ARCH_MAP_VDSO_32 0x2002 > #define ARCH_MAP_VDSO_64 0x2003 > > +#define ARCH_CET_STATUS 0x3001 > +#define ARCH_CET_DISABLE 0x3002 > +#define ARCH_CET_LOCK 0x3003 > +#define ARCH_CET_ALLOC_SHSTK 0x3004 > + > #endif /* _ASM_X86_PRCTL_H */ > diff --git a/arch/x86/kernel/Makefile b/arch/x86/kernel/Makefile > index 36b14ef410c8..b9e6cdc6b4f7 100644 > --- a/arch/x86/kernel/Makefile > +++ b/arch/x86/kernel/Makefile > @@ -139,7 +139,7 @@ obj-$(CONFIG_UNWINDER_ORC) += unwind_orc.o > obj-$(CONFIG_UNWINDER_FRAME_POINTER) += unwind_frame.o > obj-$(CONFIG_UNWINDER_GUESS) += unwind_guess.o > > -obj-$(CONFIG_X86_INTEL_CET) += cet.o > +obj-$(CONFIG_X86_INTEL_CET) += cet.o cet_prctl.o > > obj-$(CONFIG_ARCH_HAS_PROGRAM_PROPERTIES) += elf.o > > diff --git a/arch/x86/kernel/cet.c b/arch/x86/kernel/cet.c > index ce0b3b7b1160..1c2689738604 100644 > --- a/arch/x86/kernel/cet.c > +++ b/arch/x86/kernel/cet.c > @@ -110,6 +110,33 @@ static int create_rstor_token(bool ia32, unsigned long ssp, > return 0; > } > > +int cet_alloc_shstk(unsigned long *arg) > +{ > + unsigned long len = *arg; > + unsigned long addr; > + unsigned long token; > + unsigned long ssp; > + > + addr = do_mmap_locked(0, len, PROT_READ, > + MAP_ANONYMOUS | MAP_PRIVATE, VM_SHSTK); > + if (addr >= TASK_SIZE_MAX) > + return -ENOMEM; > + > + /* Restore token is 8 bytes and aligned to 8 bytes */ > + ssp = addr + len; > + token = ssp; > + > + if (!in_ia32_syscall()) > + token |= 1; This pair of check and bit or'ing definitely asks for a macro or a wrapper function. > + ssp -= 8; > + > + if (write_user_shstk_64(ssp, token)) > + return -EINVAL; Shouldn't addr be unmapped on error? > + *arg = addr; > + return 0; > +} > + > int cet_setup_shstk(void) > { > unsigned long addr, size; > diff --git a/arch/x86/kernel/cet_prctl.c b/arch/x86/kernel/cet_prctl.c > new file mode 100644 > index 000000000000..c4b7c19f5040 > --- /dev/null > +++ b/arch/x86/kernel/cet_prctl.c > @@ -0,0 +1,79 @@ > +/* SPDX-License-Identifier: GPL-2.0 */ > + > +#include <linux/errno.h> > +#include <linux/uaccess.h> > +#include <linux/prctl.h> > +#include <linux/compat.h> > +#include <asm/processor.h> > +#include <asm/prctl.h> > +#include <asm/elf.h> > +#include <asm/elf_property.h> > +#include <asm/cet.h> > + > +/* See Documentation/x86/intel_cet.txt. */ > + > +static int handle_get_status(unsigned long arg2) > +{ > + unsigned int features = 0; > + unsigned long shstk_base, shstk_size; > + unsigned long buf[3]; > + > + if (current->thread.cet.shstk_enabled) > + features |= GNU_PROPERTY_X86_FEATURE_1_SHSTK; > + > + shstk_base = current->thread.cet.shstk_base; > + shstk_size = current->thread.cet.shstk_size; > + > + buf[0] = (unsigned long)features; > + buf[1] = shstk_base; > + buf[2] = shstk_size; > + return copy_to_user((unsigned long __user *)arg2, buf, > + sizeof(buf)); > +} > + > +static int handle_alloc_shstk(unsigned long arg2) > +{ > + int err = 0; > + unsigned long shstk_size = 0; > + > + if (get_user(shstk_size, (unsigned long __user *)arg2)) > + return -EFAULT; > + > + err = cet_alloc_shstk(&shstk_size); > + if (err) > + return err; > + > + if (put_user(shstk_size, (unsigned long __user *)arg2)) Again, leaking allocated stack. > + return -EFAULT; > + > + return 0; > +} > + > +int prctl_cet(int option, unsigned long arg2) > +{ > + if (!cpu_feature_enabled(X86_FEATURE_SHSTK)) > + return -EINVAL; > + > + switch (option) { > + case ARCH_CET_STATUS: > + return handle_get_status(arg2); > + > + case ARCH_CET_DISABLE: > + if (current->thread.cet.locked) > + return -EPERM; > + if (arg2 & GNU_PROPERTY_X86_FEATURE_1_SHSTK) > + cet_disable_free_shstk(current); The rest of bits in arg2 should be 0, otherwise this interface won't be possible to extend. > + return 0; > + > + case ARCH_CET_LOCK: > + current->thread.cet.locked = 1; > + return 0; > + > + case ARCH_CET_ALLOC_SHSTK: > + return handle_alloc_shstk(arg2); > + > + default: > + return -EINVAL; > + } > +} > diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c > index 440f012ef925..251b8714f9a3 100644 > --- a/arch/x86/kernel/process.c > +++ b/arch/x86/kernel/process.c > @@ -792,6 +792,11 @@ long do_arch_prctl_common(struct task_struct *task, int option, > return get_cpuid_mode(); > case ARCH_SET_CPUID: > return set_cpuid_mode(task, cpuid_enabled); > + case ARCH_CET_STATUS: > + case ARCH_CET_DISABLE: > + case ARCH_CET_LOCK: > + case ARCH_CET_ALLOC_SHSTK: > + return prctl_cet(option, cpuid_enabled); It's probably a good opportunity to change the strange name for an argument of a dispatch call.
diff --git a/arch/x86/include/asm/cet.h b/arch/x86/include/asm/cet.h index b7b33e1026bb..212bd68e31d3 100644 --- a/arch/x86/include/asm/cet.h +++ b/arch/x86/include/asm/cet.h @@ -12,19 +12,24 @@ struct task_struct; struct cet_status { unsigned long shstk_base; unsigned long shstk_size; + unsigned int locked:1; unsigned int shstk_enabled:1; }; #ifdef CONFIG_X86_INTEL_CET +int prctl_cet(int option, unsigned long arg2); int cet_setup_shstk(void); int cet_setup_thread_shstk(struct task_struct *p); +int cet_alloc_shstk(unsigned long *arg); void cet_disable_shstk(void); void cet_disable_free_shstk(struct task_struct *p); int cet_restore_signal(unsigned long ssp); int cet_setup_signal(bool ia32, unsigned long rstor, unsigned long *new_ssp); #else +static inline int prctl_cet(int option, unsigned long arg2) { return 0; } static inline int cet_setup_shstk(void) { return 0; } static inline int cet_setup_thread_shstk(struct task_struct *p) { return 0; } +static inline int cet_alloc_shstk(unsigned long *arg) { return -EINVAL; } static inline void cet_disable_shstk(void) {} static inline void cet_disable_free_shstk(struct task_struct *p) {} static inline int cet_restore_signal(unsigned long ssp) { return 0; } diff --git a/arch/x86/include/uapi/asm/prctl.h b/arch/x86/include/uapi/asm/prctl.h index 5a6aac9fa41f..3aec1088e01d 100644 --- a/arch/x86/include/uapi/asm/prctl.h +++ b/arch/x86/include/uapi/asm/prctl.h @@ -14,4 +14,9 @@ #define ARCH_MAP_VDSO_32 0x2002 #define ARCH_MAP_VDSO_64 0x2003 +#define ARCH_CET_STATUS 0x3001 +#define ARCH_CET_DISABLE 0x3002 +#define ARCH_CET_LOCK 0x3003 +#define ARCH_CET_ALLOC_SHSTK 0x3004 + #endif /* _ASM_X86_PRCTL_H */ diff --git a/arch/x86/kernel/Makefile b/arch/x86/kernel/Makefile index 36b14ef410c8..b9e6cdc6b4f7 100644 --- a/arch/x86/kernel/Makefile +++ b/arch/x86/kernel/Makefile @@ -139,7 +139,7 @@ obj-$(CONFIG_UNWINDER_ORC) += unwind_orc.o obj-$(CONFIG_UNWINDER_FRAME_POINTER) += unwind_frame.o obj-$(CONFIG_UNWINDER_GUESS) += unwind_guess.o -obj-$(CONFIG_X86_INTEL_CET) += cet.o +obj-$(CONFIG_X86_INTEL_CET) += cet.o cet_prctl.o obj-$(CONFIG_ARCH_HAS_PROGRAM_PROPERTIES) += elf.o diff --git a/arch/x86/kernel/cet.c b/arch/x86/kernel/cet.c index ce0b3b7b1160..1c2689738604 100644 --- a/arch/x86/kernel/cet.c +++ b/arch/x86/kernel/cet.c @@ -110,6 +110,33 @@ static int create_rstor_token(bool ia32, unsigned long ssp, return 0; } +int cet_alloc_shstk(unsigned long *arg) +{ + unsigned long len = *arg; + unsigned long addr; + unsigned long token; + unsigned long ssp; + + addr = do_mmap_locked(0, len, PROT_READ, + MAP_ANONYMOUS | MAP_PRIVATE, VM_SHSTK); + if (addr >= TASK_SIZE_MAX) + return -ENOMEM; + + /* Restore token is 8 bytes and aligned to 8 bytes */ + ssp = addr + len; + token = ssp; + + if (!in_ia32_syscall()) + token |= 1; + ssp -= 8; + + if (write_user_shstk_64(ssp, token)) + return -EINVAL; + + *arg = addr; + return 0; +} + int cet_setup_shstk(void) { unsigned long addr, size; diff --git a/arch/x86/kernel/cet_prctl.c b/arch/x86/kernel/cet_prctl.c new file mode 100644 index 000000000000..c4b7c19f5040 --- /dev/null +++ b/arch/x86/kernel/cet_prctl.c @@ -0,0 +1,79 @@ +/* SPDX-License-Identifier: GPL-2.0 */ + +#include <linux/errno.h> +#include <linux/uaccess.h> +#include <linux/prctl.h> +#include <linux/compat.h> +#include <asm/processor.h> +#include <asm/prctl.h> +#include <asm/elf.h> +#include <asm/elf_property.h> +#include <asm/cet.h> + +/* See Documentation/x86/intel_cet.txt. */ + +static int handle_get_status(unsigned long arg2) +{ + unsigned int features = 0; + unsigned long shstk_base, shstk_size; + unsigned long buf[3]; + + if (current->thread.cet.shstk_enabled) + features |= GNU_PROPERTY_X86_FEATURE_1_SHSTK; + + shstk_base = current->thread.cet.shstk_base; + shstk_size = current->thread.cet.shstk_size; + + buf[0] = (unsigned long)features; + buf[1] = shstk_base; + buf[2] = shstk_size; + return copy_to_user((unsigned long __user *)arg2, buf, + sizeof(buf)); +} + +static int handle_alloc_shstk(unsigned long arg2) +{ + int err = 0; + unsigned long shstk_size = 0; + + if (get_user(shstk_size, (unsigned long __user *)arg2)) + return -EFAULT; + + err = cet_alloc_shstk(&shstk_size); + if (err) + return err; + + if (put_user(shstk_size, (unsigned long __user *)arg2)) + return -EFAULT; + + return 0; +} + +int prctl_cet(int option, unsigned long arg2) +{ + if (!cpu_feature_enabled(X86_FEATURE_SHSTK)) + return -EINVAL; + + switch (option) { + case ARCH_CET_STATUS: + return handle_get_status(arg2); + + case ARCH_CET_DISABLE: + if (current->thread.cet.locked) + return -EPERM; + if (arg2 & GNU_PROPERTY_X86_FEATURE_1_SHSTK) + cet_disable_free_shstk(current); + + return 0; + + case ARCH_CET_LOCK: + current->thread.cet.locked = 1; + return 0; + + case ARCH_CET_ALLOC_SHSTK: + return handle_alloc_shstk(arg2); + + default: + return -EINVAL; + } +} diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c index 440f012ef925..251b8714f9a3 100644 --- a/arch/x86/kernel/process.c +++ b/arch/x86/kernel/process.c @@ -792,6 +792,11 @@ long do_arch_prctl_common(struct task_struct *task, int option, return get_cpuid_mode(); case ARCH_SET_CPUID: return set_cpuid_mode(task, cpuid_enabled); + case ARCH_CET_STATUS: + case ARCH_CET_DISABLE: + case ARCH_CET_LOCK: + case ARCH_CET_ALLOC_SHSTK: + return prctl_cet(option, cpuid_enabled); } return -EINVAL;
arch_prctl(ARCH_CET_STATUS, unsigned long *addr) Return CET feature status. The parameter 'addr' is a pointer to a user buffer. On returning to the caller, the kernel fills the following information: *addr = SHSTK/IBT status *(addr + 1) = SHSTK base address *(addr + 2) = SHSTK size arch_prctl(ARCH_CET_DISABLE, unsigned long features) Disable CET features specified in 'features'. Return -EPERM if CET is locked. arch_prctl(ARCH_CET_LOCK) Lock in CET feature. arch_prctl(ARCH_CET_ALLOC_SHSTK, unsigned long *addr) Allocate a new SHSTK. The parameter 'addr' is a pointer to a user buffer and indicates the desired SHSTK size to allocate. On returning to the caller the buffer contains the address of the new SHSTK. Signed-off-by: H.J. Lu <hjl.tools@gmail.com> Signed-off-by: Yu-cheng Yu <yu-cheng.yu@intel.com> --- arch/x86/include/asm/cet.h | 5 ++ arch/x86/include/uapi/asm/prctl.h | 5 ++ arch/x86/kernel/Makefile | 2 +- arch/x86/kernel/cet.c | 27 +++++++++++ arch/x86/kernel/cet_prctl.c | 79 +++++++++++++++++++++++++++++++ arch/x86/kernel/process.c | 5 ++ 6 files changed, 122 insertions(+), 1 deletion(-) create mode 100644 arch/x86/kernel/cet_prctl.c