copy_msg_from_user() and copy_msg_to_user()
- copies a mesage from/to userspace without need of translating addresses - the assumption is that the address space is installed, i.e. ldt and cr3 are loaded correctly - if a pagefault or a general protection occurs while copying from userland to kernel (or vice versa) and error is returned which gives the caller a chance to respond in a proper way - error happens _only_ because of a wrong user pointer if the function is used correctly - if the prerequisites of the function do no hold, the function will most likely fail as the user address becomes random
This commit is contained in:
Tomas Hruby
parent
ad9ba944d1
commit
5e57818431
4 changed files with 167 additions and 0 deletions
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@ -142,6 +142,33 @@ PUBLIC void exception_handler(int is_nested, struct exception_frame * frame)
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return;
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}
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/*
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* handle special cases for nested problems as they might be tricky or filter
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* them out quickly if the traps are not nested
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*/
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if (is_nested) {
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/*
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* if a problem occured while copying a message from userspace because
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* of a wrong pointer supplied by userland, handle it the only way we
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* can handle it ...
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*/
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if (((void*)frame->eip >= copy_msg_to_user &&
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(void*)frame->eip <= __copy_msg_to_user_end) ||
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((void*)frame->eip >= copy_msg_from_user &&
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(void*)frame->eip <= __copy_msg_from_user_end)) {
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switch(frame->vector) {
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/* these error are expected */
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case PAGE_FAULT_VECTOR:
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case PROTECTION_VECTOR:
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frame->eip = (reg_t) __user_copy_msg_pointer_failure;
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return;
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default:
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minix_panic("Copy involving a user pointer "
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"failed unexpectedly!", NO_NUM);
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}
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}
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}
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if(frame->vector == PAGE_FAULT_VECTOR) {
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pagefault(saved_proc, frame, is_nested);
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return;
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@ -386,6 +386,137 @@ phys_copy_fault_in_kernel: /* kernel can send us here */
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mov %cr2, %eax
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ret
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/*===========================================================================*/
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/* copy_msg_from_user */
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/*===========================================================================*/
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/*
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* int copy_msg_from_user(struct proc * p, message * user_mbuf, message * dst);
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*
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* Copies a message of 36 bytes from user process space to a kernel buffer. This
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* function assumes that the process address space is installed (cr3 loaded) and
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* the local descriptor table of this process is loaded too.
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*
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* The %gs segment register is used to access the userspace memory. We load the
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* process' data segment in this register.
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*
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* This function from the callers point of view either succeeds or returns an
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* error which gives the caller a chance to respond accordingly. In fact it
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* either succeeds or if it generates a pagefault, general protection or other
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* exception, the trap handler has to redirect the execution to
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* __user_copy_msg_pointer_failure where the error is reported to the caller
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* without resolving the pagefault. It is not kernel's problem to deal with
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* wrong pointers from userspace and the caller should return an error to
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* userspace as if wrong values or request were passed to the kernel
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*/
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.balign 16
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.globl copy_msg_from_user
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copy_msg_from_user:
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push %gs
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mov 8(%esp), %eax
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movw DSREG(%eax), %gs
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/* load the source pointer */
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mov 12(%esp), %ecx
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/* load the destination pointer */
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mov 16(%esp), %edx
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mov %gs:0*4(%ecx), %eax
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mov %eax, 0*4(%edx)
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mov %gs:1*4(%ecx), %eax
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mov %eax, 1*4(%edx)
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mov %gs:2*4(%ecx), %eax
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mov %eax, 2*4(%edx)
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mov %gs:3*4(%ecx), %eax
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mov %eax, 3*4(%edx)
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mov %gs:4*4(%ecx), %eax
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mov %eax, 4*4(%edx)
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mov %gs:5*4(%ecx), %eax
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mov %eax, 5*4(%edx)
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mov %gs:6*4(%ecx), %eax
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mov %eax, 6*4(%edx)
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mov %gs:7*4(%ecx), %eax
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mov %eax, 7*4(%edx)
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mov %gs:8*4(%ecx), %eax
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mov %eax, 8*4(%edx)
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.globl __copy_msg_from_user_end
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__copy_msg_from_user_end:
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pop %gs
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movl $0, %eax
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ret
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/*===========================================================================*/
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/* copy_msg_to_user */
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/*===========================================================================*/
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/*
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* void copy_msg_to_user(struct proc * p, message * src, message * user_mbuf);
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*
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* Copies a message of 36 bytes to user process space from a kernel buffer. This
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* function assumes that the process address space is installed (cr3 loaded) and
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* the local descriptor table of this process is loaded too.
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*
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* All the other copy_msg_from_user() comments apply here as well!
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*/
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.balign 16
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.globl copy_msg_to_user
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copy_msg_to_user:
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push %gs
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mov 8(%esp), %eax
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movw DSREG(%eax), %gs
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/* load the source pointer */
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mov 12(%esp), %ecx
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/* load the destination pointer */
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mov 16(%esp), %edx
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mov 0*4(%ecx), %eax
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mov %eax, %gs:0*4(%edx)
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mov 1*4(%ecx), %eax
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mov %eax, %gs:1*4(%edx)
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mov 2*4(%ecx), %eax
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mov %eax, %gs:2*4(%edx)
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mov 3*4(%ecx), %eax
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mov %eax, %gs:3*4(%edx)
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mov 4*4(%ecx), %eax
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mov %eax, %gs:4*4(%edx)
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mov 5*4(%ecx), %eax
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mov %eax, %gs:5*4(%edx)
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mov 6*4(%ecx), %eax
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mov %eax, %gs:6*4(%edx)
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mov 7*4(%ecx), %eax
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mov %eax, %gs:7*4(%edx)
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mov 8*4(%ecx), %eax
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mov %eax, %gs:8*4(%edx)
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.globl __copy_msg_to_user_end
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__copy_msg_to_user_end:
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pop %gs
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movl $0, %eax
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ret
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/*
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* if a function from a selected set of copies from or to userspace fails, it is
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* because of a wrong pointer supplied by the userspace. We have to clean up and
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* and return -1 to indicated that something wrong has happend. The place it was
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* called from has to handle this situation. The exception handler redirect us
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* here to continue, clean up and report the error
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*/
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.balign 16
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.globl __user_copy_msg_pointer_failure
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__user_copy_msg_pointer_failure:
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pop %gs
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movl $-1, %eax
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ret
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/*===========================================================================*/
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/* phys_memset */
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/*===========================================================================*/
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@ -44,6 +44,7 @@ void _PROTOTYPE( simd_exception, (void) );
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/* Software interrupt handlers, in numerical order. */
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_PROTOTYPE( void trp, (void) );
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_PROTOTYPE( void ipc_entry, (void) );
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_PROTOTYPE( void kernel_call_entry, (void) );
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_PROTOTYPE( void level0_call, (void) );
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/* memory.c */
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@ -153,6 +154,10 @@ EXTERN void * k_boot_stktop;
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_PROTOTYPE( void int_gate, (unsigned vec_nr, vir_bytes offset,
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unsigned dpl_type) );
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_PROTOTYPE(void __copy_msg_from_user_end, (void));
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_PROTOTYPE(void __copy_msg_to_user_end, (void));
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_PROTOTYPE(void __user_copy_msg_pointer_failure, (void));
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/* functions defined in architecture-independent kernel source. */
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#include "../../proto.h"
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@ -171,5 +171,9 @@ _PROTOTYPE( int arch_phys_map, (int index, phys_bytes *addr,
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_PROTOTYPE( int arch_phys_map_reply, (int index, vir_bytes addr));
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_PROTOTYPE( int arch_enable_paging, (void));
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_PROTOTYPE( int copy_msg_from_user, (struct proc * p, message * user_mbuf,
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message * dst));
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_PROTOTYPE( int copy_msg_to_user, (struct proc * p, message * src,
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message * user_mbuf));
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_PROTOTYPE(void switch_address_space, (struct proc * p));
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#endif /* PROTO_H */
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