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minix/kernel/system/do_safecopy.c
Ben Gras cd8b915ed9 Primary goal for these changes is: 
- no longer have kernel have its own page table that is loaded
    on every kernel entry (trap, interrupt, exception). the primary
    purpose is to reduce the number of required reloads.
Result:
  - kernel can only access memory of process that was running when
    kernel was entered
  - kernel must be mapped into every process page table, so traps to
    kernel keep working
Problem:
  - kernel must often access memory of arbitrary processes (e.g. send
    arbitrary processes messages); this can't happen directly any more;
    usually because that process' page table isn't loaded at all, sometimes
    because that memory isn't mapped in at all, sometimes because it isn't
    mapped in read-write.
So:
  - kernel must be able to map in memory of any process, in its own
    address space.
Implementation:
  - VM and kernel share a range of memory in which addresses of
    all page tables of all processes are available. This has two purposes:
      . Kernel has to know what data to copy in order to map in a range
      . Kernel has to know where to write the data in order to map it in
    That last point is because kernel has to write in the currently loaded
    page table.
  - Processes and kernel are separated through segments; kernel segments
    haven't changed.
  - The kernel keeps the process whose page table is currently loaded
    in 'ptproc.'
  - If it wants to map in a range of memory, it writes the value of the
    page directory entry for that range into the page directory entry
    in the currently loaded map. There is a slot reserved for such
    purposes. The kernel can then access this memory directly.
  - In order to do this, its segment has been increased (and the
    segments of processes start where it ends).
  - In the pagefault handler, detect if the kernel is doing
    'trappable' memory access (i.e. a pagefault isn't a fatal
     error) and if so,
       - set the saved instruction pointer to phys_copy_fault,
	 breaking out of phys_copy
       - set the saved eax register to the address of the page
	 fault, both for sanity checking and for checking in
	 which of the two ranges that phys_copy was called
	 with the fault occured
  - Some boot-time processes do not have their own page table,
    and are mapped in with the kernel, and separated with
    segments. The kernel detects this using HASPT. If such a
    process has to be scheduled, any page table will work and
    no page table switch is done.

Major changes in kernel are
  - When accessing user processes memory, kernel no longer
    explicitly checks before it does so if that memory is OK.
    It simply makes the mapping (if necessary), tries to do the
    operation, and traps the pagefault if that memory isn't present;
    if that happens, the copy function returns EFAULT.
    So all of the CHECKRANGE_OR_SUSPEND macros are gone.
  - Kernel no longer has to copy/read and parse page tables.
  - A message copying optimisation: when messages are copied, and
    the recipient isn't mapped in, they are copied into a buffer
    in the kernel. This is done in QueueMess. The next time
    the recipient is scheduled, this message is copied into
    its memory. This happens in schedcheck().
    This eliminates the mapping/copying step for messages, and makes
    it easier to deliver messages. This eliminates soft_notify.
  - Kernel no longer creates a page table at all, so the vm_setbuf
    and pagetable writing in memory.c is gone.

Minor changes in kernel are
  - ipc_stats thrown out, wasn't used
  - misc flags all renamed to MF_*
  - NOREC_* macros to enter and leave functions that should not
    be called recursively; just sanity checks really
  - code to fully decode segment selectors and descriptors
    to print on exceptions
  - lots of vmassert()s added, only executed if DEBUG_VMASSERT is 1
2009-09-21 14:31:52 +00:00

323 lines
9.3 KiB
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/* The kernel call implemented in this file:
* m_type: SYS_SAFECOPYFROM or SYS_SAFECOPYTO or SYS_VSAFECOPY
*
* The parameters for this kernel call are:
* SCP_FROM_TO other endpoint
* SCP_INFO encoded: caller's own src/dst segment
* SCP_GID grant id
* SCP_OFFSET offset within granted space
* SCP_ADDRESS address in own address space
* SCP_BYTES bytes to be copied
*
* For the vectored variant (do_vsafecopy):
* VSCP_VEC_ADDR address of vector
* VSCP_VEC_SIZE number of significant elements in vector
*/
#include <minix/type.h>
#include <minix/safecopies.h>
#include "../system.h"
#include "../vm.h"
#define MEM_TOP 0xFFFFFFFFUL
FORWARD _PROTOTYPE(int safecopy, (endpoint_t, endpoint_t, cp_grant_id_t, int, int, size_t, vir_bytes, vir_bytes, int));
#define HASGRANTTABLE(gr) \
(!RTS_ISSET(gr, NO_PRIV) && priv(gr) && priv(gr)->s_grant_table > 0)
/*===========================================================================*
* verify_grant *
*===========================================================================*/
PUBLIC int verify_grant(granter, grantee, grant, bytes, access,
offset_in, offset_result, e_granter)
endpoint_t granter, grantee; /* copyee, copyer */
cp_grant_id_t grant; /* grant id */
vir_bytes bytes; /* copy size */
int access; /* direction (read/write) */
vir_bytes offset_in; /* copy offset within grant */
vir_bytes *offset_result; /* copy offset within virtual address space */
endpoint_t *e_granter; /* new granter (magic grants) */
{
static cp_grant_t g;
static int proc_nr;
static struct proc *granter_proc;
int r;
/* Get granter process slot (if valid), and check range of
* grant id.
*/
if(!isokendpt(granter, &proc_nr) || !GRANT_VALID(grant)) {
kprintf("grant verify failed: invalid granter or grant\n");
return(EINVAL);
}
granter_proc = proc_addr(proc_nr);
/* If there is no priv. structure, or no grant table in the
* priv. structure, or the grant table in the priv. structure
* is too small for the grant, return EPERM.
*/
if(!HASGRANTTABLE(granter_proc)) return EPERM;
if(priv(granter_proc)->s_grant_entries <= grant) {
kprintf(
"verify_grant: grant verify failed in ep %d proc %d: "
"grant %d out of range for table size %d\n",
granter, proc_nr, grant,
priv(granter_proc)->s_grant_entries);
return(EPERM);
}
/* Copy the grant entry corresponding to this id to see what it
* looks like. If it fails, hide the fact that granter has
* (presumably) set an invalid grant table entry by returning
* EPERM, just like with an invalid grant id.
*/
if((r=data_copy(granter,
priv(granter_proc)->s_grant_table + sizeof(g)*grant,
SYSTEM, (vir_bytes) &g, sizeof(g))) != OK) {
kprintf("verify_grant: grant verify: data_copy failed\n");
return EPERM;
}
/* Check validity. */
if((g.cp_flags & (CPF_USED | CPF_VALID)) != (CPF_USED | CPF_VALID)) {
kprintf(
"verify_grant: grant failed: invalid (%d flags 0x%lx)\n",
grant, g.cp_flags);
return EPERM;
}
/* Check access of grant. */
if(((g.cp_flags & access) != access)) {
kprintf(
"verify_grant: grant verify failed: access invalid; want 0x%x, have 0x%x\n",
access, g.cp_flags);
return EPERM;
}
if((g.cp_flags & CPF_DIRECT)) {
/* Don't fiddle around with grants that wrap, arithmetic
* below may be confused.
*/
if(MEM_TOP - g.cp_u.cp_direct.cp_len <
g.cp_u.cp_direct.cp_start - 1) {
kprintf(
"verify_grant: direct grant verify failed: len too long\n");
return EPERM;
}
/* Verify actual grantee. */
if(g.cp_u.cp_direct.cp_who_to != grantee && grantee != ANY) {
kprintf(
"verify_grant: direct grant verify failed: bad grantee\n");
return EPERM;
}
/* Verify actual copy range. */
if((offset_in+bytes < offset_in) ||
offset_in+bytes > g.cp_u.cp_direct.cp_len) {
kprintf(
"verify_grant: direct grant verify failed: bad size or range. "
"granted %d bytes @ 0x%lx; wanted %d bytes @ 0x%lx\n",
g.cp_u.cp_direct.cp_len,
g.cp_u.cp_direct.cp_start,
bytes, offset_in);
return EPERM;
}
/* Verify successful - tell caller what address it is. */
*offset_result = g.cp_u.cp_direct.cp_start + offset_in;
*e_granter = granter;
} else if(g.cp_flags & CPF_MAGIC) {
/* Currently, it is hardcoded that only FS may do
* magic grants.
*/
if(granter != FS_PROC_NR) {
kprintf(
"verify_grant: magic grant verify failed: granter (%d) "
"is not FS (%d)\n", granter, FS_PROC_NR);
return EPERM;
}
/* Verify actual grantee. */
if(g.cp_u.cp_magic.cp_who_to != grantee && grantee != ANY) {
kprintf(
"verify_grant: magic grant verify failed: bad grantee\n");
return EPERM;
}
/* Verify actual copy range. */
if((offset_in+bytes < offset_in) ||
offset_in+bytes > g.cp_u.cp_magic.cp_len) {
kprintf(
"verify_grant: magic grant verify failed: bad size or range. "
"granted %d bytes @ 0x%lx; wanted %d bytes @ 0x%lx\n",
g.cp_u.cp_magic.cp_len,
g.cp_u.cp_magic.cp_start,
bytes, offset_in);
return EPERM;
}
/* Verify successful - tell caller what address it is. */
*offset_result = g.cp_u.cp_magic.cp_start + offset_in;
*e_granter = g.cp_u.cp_magic.cp_who_from;
} else {
kprintf(
"verify_grant: grant verify failed: unknown grant type\n");
return EPERM;
}
return OK;
}
/*===========================================================================*
* safecopy *
*===========================================================================*/
PRIVATE int safecopy(granter, grantee, grantid, src_seg, dst_seg, bytes,
g_offset, addr, access)
endpoint_t granter, grantee;
cp_grant_id_t grantid;
int src_seg, dst_seg;
size_t bytes;
vir_bytes g_offset, addr;
int access; /* CPF_READ for a copy from granter to grantee, CPF_WRITE
* for a copy from grantee to granter.
*/
{
static struct vir_addr v_src, v_dst;
static vir_bytes v_offset;
int r;
endpoint_t new_granter, *src, *dst;
struct proc *granter_p;
/* See if there is a reasonable grant table. */
if(!(granter_p = endpoint_lookup(granter))) return EINVAL;
if(!HASGRANTTABLE(granter_p)) return EPERM;
/* Decide who is src and who is dst. */
if(access & CPF_READ) {
src = &granter;
dst = &grantee;
} else {
src = &grantee;
dst = &granter;
}
/* Verify permission exists. */
if((r=verify_grant(granter, grantee, grantid, bytes, access,
g_offset, &v_offset, &new_granter)) != OK) {
kprintf(
"grant %d verify to copy %d->%d by %d failed: err %d\n",
grantid, *src, *dst, grantee, r);
return r;
}
/* verify_grant() can redirect the grantee to someone else,
* meaning the source or destination changes.
*/
granter = new_granter;
/* Now it's a regular copy. */
v_src.segment = src_seg;
v_dst.segment = dst_seg;
v_src.proc_nr_e = *src;
v_dst.proc_nr_e = *dst;
/* Now the offset in virtual addressing is known in 'offset'.
* Depending on the access, this is the source or destination
* address.
*/
if(access & CPF_READ) {
v_src.offset = v_offset;
v_dst.offset = (vir_bytes) addr;
} else {
v_src.offset = (vir_bytes) addr;
v_dst.offset = v_offset;
}
/* Do the regular copy. */
return virtual_copy_vmcheck(&v_src, &v_dst, bytes);
}
/*===========================================================================*
* do_safecopy *
*===========================================================================*/
PUBLIC int do_safecopy(m_ptr)
register message *m_ptr; /* pointer to request message */
{
static int access, src_seg, dst_seg;
/* Set src and dst parameters.
* The caller's seg is encoded in the SCP_INFO field.
*/
if(sys_call_code == SYS_SAFECOPYFROM) {
src_seg = D;
dst_seg = SCP_INFO2SEG(m_ptr->SCP_INFO);
access = CPF_READ;
} else if(sys_call_code == SYS_SAFECOPYTO) {
src_seg = SCP_INFO2SEG(m_ptr->SCP_INFO);
dst_seg = D;
access = CPF_WRITE;
} else minix_panic("Impossible system call nr. ", sys_call_code);
return safecopy(m_ptr->SCP_FROM_TO, who_e, m_ptr->SCP_GID,
src_seg, dst_seg, m_ptr->SCP_BYTES, m_ptr->SCP_OFFSET,
(vir_bytes) m_ptr->SCP_ADDRESS, access);
}
/*===========================================================================*
* do_vsafecopy *
*===========================================================================*/
PUBLIC int do_vsafecopy(m_ptr)
register message *m_ptr; /* pointer to request message */
{
static struct vscp_vec vec[SCPVEC_NR];
static struct vir_addr src, dst;
int r, i, els;
size_t bytes;
/* Set vector copy parameters. */
src.proc_nr_e = who_e;
src.offset = (vir_bytes) m_ptr->VSCP_VEC_ADDR;
src.segment = dst.segment = D;
dst.proc_nr_e = SYSTEM;
dst.offset = (vir_bytes) vec;
/* No. of vector elements. */
els = m_ptr->VSCP_VEC_SIZE;
bytes = els * sizeof(struct vscp_vec);
/* Obtain vector of copies. */
if((r=virtual_copy_vmcheck(&src, &dst, bytes)) != OK)
return r;
/* Perform safecopies. */
for(i = 0; i < els; i++) {
int access;
endpoint_t granter;
if(vec[i].v_from == SELF) {
access = CPF_WRITE;
granter = vec[i].v_to;
} else if(vec[i].v_to == SELF) {
access = CPF_READ;
granter = vec[i].v_from;
} else {
kprintf("vsafecopy: %d: element %d/%d: no SELF found\n",
who_e, i, els);
return EINVAL;
}
/* Do safecopy for this element. */
if((r=safecopy(granter, who_e, vec[i].v_gid, D, D,
vec[i].v_bytes, vec[i].v_offset,
vec[i].v_addr, access)) != OK) {
return r;
}
}
return OK;
}
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