Commit db85be57 authored by Paul Mackerras's avatar Paul Mackerras

PPC32: Better check for when we should expand the stack.

parent e106935f
...@@ -56,6 +56,41 @@ void bad_page_fault(struct pt_regs *, unsigned long, int sig); ...@@ -56,6 +56,41 @@ void bad_page_fault(struct pt_regs *, unsigned long, int sig);
void do_page_fault(struct pt_regs *, unsigned long, unsigned long); void do_page_fault(struct pt_regs *, unsigned long, unsigned long);
extern int get_pteptr(struct mm_struct *mm, unsigned long addr, pte_t **ptep); extern int get_pteptr(struct mm_struct *mm, unsigned long addr, pte_t **ptep);
/*
* Check whether the instruction at regs->nip is a store using
* an update addressing form which will update r1.
*/
static int store_updates_sp(struct pt_regs *regs)
{
unsigned int inst;
if (get_user(inst, (unsigned int *)regs->nip))
return 0;
/* check for 1 in the rA field */
if (((inst >> 16) & 0x1f) != 1)
return 0;
/* check major opcode */
switch (inst >> 26) {
case 37: /* stwu */
case 39: /* stbu */
case 45: /* sthu */
case 53: /* stfsu */
case 55: /* stfdu */
return 1;
case 31:
/* check minor opcode */
switch ((inst >> 1) & 0x3ff) {
case 183: /* stwux */
case 247: /* stbux */
case 439: /* sthux */
case 695: /* stfsux */
case 759: /* stfdux */
return 1;
}
}
return 0;
}
/* /*
* For 600- and 800-family processors, the error_code parameter is DSISR * For 600- and 800-family processors, the error_code parameter is DSISR
* for a data fault, SRR1 for an instruction fault. For 400-family processors * for a data fault, SRR1 for an instruction fault. For 400-family processors
...@@ -112,6 +147,40 @@ void do_page_fault(struct pt_regs *regs, unsigned long address, ...@@ -112,6 +147,40 @@ void do_page_fault(struct pt_regs *regs, unsigned long address,
goto good_area; goto good_area;
if (!(vma->vm_flags & VM_GROWSDOWN)) if (!(vma->vm_flags & VM_GROWSDOWN))
goto bad_area; goto bad_area;
if (!is_write)
goto bad_area;
/*
* N.B. The rs6000/xcoff ABI allows programs to access up to
* a few hundred bytes below the stack pointer.
* The kernel signal delivery code writes up to about 1.5kB
* below the stack pointer (r1) before decrementing it.
* The exec code can write slightly over 640kB to the stack
* before setting the user r1. Thus we allow the stack to
* expand to 1MB without further checks.
*/
if (address + 0x100000 < vma->vm_end) {
/* get user regs even if this fault is in kernel mode */
struct pt_regs *uregs = current->thread.regs;
if (uregs == NULL)
goto bad_area;
/*
* A user-mode access to an address a long way below
* the stack pointer is only valid if the instruction
* is one which would update the stack pointer to the
* address accessed if the instruction completed,
* i.e. either stwu rs,n(r1) or stwux rs,r1,rb
* (or the byte, halfword, float or double forms).
*
* If we don't check this then any write to the area
* between the last mapped region and the stack will
* expand the stack rather than segfaulting.
*/
if (address + 2048 < uregs->gpr[1]
&& (!user_mode(regs) || !store_updates_sp(regs)))
goto bad_area;
}
if (expand_stack(vma, address)) if (expand_stack(vma, address))
goto bad_area; goto bad_area;
......
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