Creation of a new hook to let LSM modules handle user-space pagefaults on x86. It can be used to avoid segfaulting the originating process. If it's the case it can modify process registers before returning.
Signed-off-by: Salvatore Mesoraca <[email protected]> Cc: [email protected] Cc: Ingo Molnar <[email protected]> --- arch/x86/mm/fault.c | 6 ++++++ include/linux/lsm_hooks.h | 9 +++++++++ include/linux/security.h | 11 +++++++++++ security/security.c | 11 +++++++++++ 4 files changed, 37 insertions(+) diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c index 8ad91a0..b75b81a 100644 --- a/arch/x86/mm/fault.c +++ b/arch/x86/mm/fault.c @@ -15,6 +15,7 @@ #include <linux/prefetch.h> /* prefetchw */ #include <linux/context_tracking.h> /* exception_enter(), ... */ #include <linux/uaccess.h> /* faulthandler_disabled() */ +#include <linux/security.h> /* security_pagefault_handler */ #include <asm/cpufeature.h> /* boot_cpu_has, ... */ #include <asm/traps.h> /* dotraplinkage, ... */ @@ -1358,6 +1359,11 @@ static inline bool smap_violation(int error_code, struct pt_regs *regs) local_irq_enable(); } + if (unlikely(security_pagefault_handler_x86(regs, + error_code, + address))) + return; + perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS, 1, regs, address); if (error_code & PF_WRITE) diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h index 6934cc5..a42c2f8 100644 --- a/include/linux/lsm_hooks.h +++ b/include/linux/lsm_hooks.h @@ -487,6 +487,11 @@ * Check if the requested @vmflags are allowed. * @vmflags contains requested the vmflags. * Return 0 if the operation is allowed to continue. + * @pagefault_handler_x86: + * Handle pagefaults on x86. + * @regs contains process' registers. + * @error_code contains error code for the pagefault. + * @address contains the address that caused the pagefault. * @file_lock: * Check permission before performing file locking operations. * Note: this hook mediates both flock and fcntl style locks. @@ -1487,6 +1492,9 @@ int (*file_mprotect)(struct vm_area_struct *vma, unsigned long reqprot, unsigned long prot); int (*check_vmflags)(vm_flags_t vmflags); + int (*pagefault_handler_x86)(struct pt_regs *regs, + unsigned long error_code, + unsigned long address); int (*file_lock)(struct file *file, unsigned int cmd); int (*file_fcntl)(struct file *file, unsigned int cmd, unsigned long arg); @@ -1759,6 +1767,7 @@ struct security_hook_heads { struct list_head mmap_file; struct list_head file_mprotect; struct list_head check_vmflags; + struct list_head pagefault_handler_x86; struct list_head file_lock; struct list_head file_fcntl; struct list_head file_set_fowner; diff --git a/include/linux/security.h b/include/linux/security.h index 67e33b6..bc38c83 100644 --- a/include/linux/security.h +++ b/include/linux/security.h @@ -303,6 +303,9 @@ int security_mmap_file(struct file *file, unsigned long prot, int security_file_mprotect(struct vm_area_struct *vma, unsigned long reqprot, unsigned long prot); int security_check_vmflags(vm_flags_t vmflags); +int __maybe_unused security_pagefault_handler_x86(struct pt_regs *regs, + unsigned long error_code, + unsigned long address); int security_file_lock(struct file *file, unsigned int cmd); int security_file_fcntl(struct file *file, unsigned int cmd, unsigned long arg); void security_file_set_fowner(struct file *file); @@ -836,6 +839,14 @@ static inline int security_check_vmflags(vm_flags_t vmflags) return 0; } +static inline int __maybe_unused security_pagefault_handler_x86( + struct pt_regs *regs, + unsigned long error_code, + unsigned long address) +{ + return 0; +} + static inline int security_file_lock(struct file *file, unsigned int cmd) { return 0; diff --git a/security/security.c b/security/security.c index 25d58f0..cf15686 100644 --- a/security/security.c +++ b/security/security.c @@ -910,6 +910,17 @@ int security_check_vmflags(vm_flags_t vmflags) return call_int_hook(check_vmflags, 0, vmflags); } +int __maybe_unused security_pagefault_handler_x86(struct pt_regs *regs, + unsigned long error_code, + unsigned long address) +{ + return call_int_hook(pagefault_handler_x86, + 0, + regs, + error_code, + address); +} + int security_file_lock(struct file *file, unsigned int cmd) { return call_int_hook(file_lock, 0, file, cmd); -- 1.9.1
