Currently the page fault handler on the x86 can get a clobbered value
for %cr2 if an interrupt occurs and causes another page fault (interrupt
handler touches a vmalloced area for example) before %cr2 is read. This
patch changes the page fault and alignment check (currently unused)
handlers to interrupt gates so that %cr2 can be read before an interrupt
can occur. I'm not certain how much of a problem this really is, but I
suspect it could cause random seg faults to user space under heavy
interrupt load. Comments are welcome.
diff -urN linux-2.4.5-pre1/arch/i386/kernel/entry.S linux/arch/i386/kernel/entry.S
--- linux-2.4.5-pre1/arch/i386/kernel/entry.S Wed Nov 8 20:09:50 2000
+++ linux/arch/i386/kernel/entry.S Sat May 5 16:32:42 2001
@@ -296,20 +296,21 @@
pushl %ds
pushl %eax
xorl %eax,%eax
+error_code_cr2:
pushl %ebp
pushl %edi
pushl %esi
pushl %edx
- decl %eax # eax = -1
pushl %ecx
pushl %ebx
cld
movl %es,%ecx
movl ORIG_EAX(%esp), %esi # get the error code
movl ES(%esp), %edi # get the function address
- movl %eax, ORIG_EAX(%esp)
+ movl $-1, ORIG_EAX(%esp)
movl %ecx, ES(%esp)
movl %esp,%edx
+ pushl %eax # push address (cr2)
pushl %esi # push the error code
pushl %edx # push the pt_regs pointer
movl $(__KERNEL_DS),%edx
@@ -317,7 +318,7 @@
movl %edx,%es
GET_CURRENT(%ebx)
call *%edi
- addl $8,%esp
+ addl $12,%esp
jmp ret_from_exception
ENTRY(coprocessor_error)
@@ -405,11 +406,18 @@
ENTRY(alignment_check)
pushl $ SYMBOL_NAME(do_alignment_check)
- jmp error_code
+ jmp get_cr2
ENTRY(page_fault)
pushl $ SYMBOL_NAME(do_page_fault)
- jmp error_code
+get_cr2:
+ pushl %ds
+ pushl %eax
+ movl %cr2,%eax
+ testl $IF_MASK,EFLAGS-EAX(%esp)
+ jz error_code_cr2
+ sti
+ jmp error_code_cr2
ENTRY(machine_check)
pushl $0
diff -urN linux-2.4.5-pre1/arch/i386/kernel/traps.c linux/arch/i386/kernel/traps.c
--- linux-2.4.5-pre1/arch/i386/kernel/traps.c Mon Mar 19 21:23:40 2001
+++ linux/arch/i386/kernel/traps.c Sat May 5 16:03:22 2001
@@ -225,15 +225,6 @@
die(str, regs, err);
}
-static inline unsigned long get_cr2(void)
-{
- unsigned long address;
-
- /* get the address */
- __asm__("movl %%cr2,%0":"=r" (address));
- return address;
-}
-
static void inline do_trap(int trapnr, int signr, char *str, int vm86,
struct pt_regs * regs, long error_code, siginfo_t *info)
{
@@ -270,13 +261,13 @@
}
#define DO_ERROR(trapnr, signr, str, name) \
-asmlinkage void do_##name(struct pt_regs * regs, long error_code) \
+asmlinkage void do_##name(struct pt_regs * regs, long error_code, unsigned long
+address) \
{ \
do_trap(trapnr, signr, str, 0, regs, error_code, NULL); \
}
#define DO_ERROR_INFO(trapnr, signr, str, name, sicode, siaddr) \
-asmlinkage void do_##name(struct pt_regs * regs, long error_code) \
+asmlinkage void do_##name(struct pt_regs * regs, long error_code, unsigned long
+address) \
{ \
siginfo_t info; \
info.si_signo = signr; \
@@ -287,13 +278,13 @@
}
#define DO_VM86_ERROR(trapnr, signr, str, name) \
-asmlinkage void do_##name(struct pt_regs * regs, long error_code) \
+asmlinkage void do_##name(struct pt_regs * regs, long error_code, unsigned long
+address) \
{ \
do_trap(trapnr, signr, str, 1, regs, error_code, NULL); \
}
#define DO_VM86_ERROR_INFO(trapnr, signr, str, name, sicode, siaddr) \
-asmlinkage void do_##name(struct pt_regs * regs, long error_code) \
+asmlinkage void do_##name(struct pt_regs * regs, long error_code, unsigned long
+address) \
{ \
siginfo_t info; \
info.si_signo = signr; \
@@ -314,7 +305,7 @@
DO_ERROR(10, SIGSEGV, "invalid TSS", invalid_TSS)
DO_ERROR(11, SIGBUS, "segment not present", segment_not_present)
DO_ERROR(12, SIGBUS, "stack segment", stack_segment)
-DO_ERROR_INFO(17, SIGBUS, "alignment check", alignment_check, BUS_ADRALN, get_cr2())
+DO_ERROR_INFO(17, SIGBUS, "alignment check", alignment_check, BUS_ADRALN, address)
asmlinkage void do_general_protection(struct pt_regs * regs, long error_code)
{
@@ -973,10 +964,10 @@
set_trap_gate(11,&segment_not_present);
set_trap_gate(12,&stack_segment);
set_trap_gate(13,&general_protection);
- set_trap_gate(14,&page_fault);
+ set_intr_gate(14,&page_fault);
set_trap_gate(15,&spurious_interrupt_bug);
set_trap_gate(16,&coprocessor_error);
- set_trap_gate(17,&alignment_check);
+ set_intr_gate(17,&alignment_check);
set_trap_gate(18,&machine_check);
set_trap_gate(19,&simd_coprocessor_error);
diff -urN linux-2.4.5-pre1/arch/i386/mm/fault.c linux/arch/i386/mm/fault.c
--- linux-2.4.5-pre1/arch/i386/mm/fault.c Wed May 2 09:24:09 2001
+++ linux/arch/i386/mm/fault.c Sat May 5 17:34:41 2001
@@ -103,19 +103,15 @@
* bit 1 == 0 means read, 1 means write
* bit 2 == 0 means kernel, 1 means user-mode
*/
-asmlinkage void do_page_fault(struct pt_regs *regs, unsigned long error_code)
+asmlinkage void do_page_fault(struct pt_regs *regs, unsigned long error_code,
+unsigned long address)
{
struct task_struct *tsk;
struct mm_struct *mm;
struct vm_area_struct * vma;
- unsigned long address;
unsigned long page;
unsigned long fixup;
int write;
siginfo_t info;
-
- /* get the address */
- __asm__("movl %%cr2,%0":"=r" (address));
tsk = current;
