[patch 01/52] [PATCH] Improve address space check.

Martin Schwidefsky
2009-11-13T15:20:17Z

[-- Attachment #1: 100-mm-check-space.diff --]
[-- Type: text/plain, Size: 8147 bytes --]

From: Martin Schwidefsky <schwidefsky@de.ibm.com>

A data access in access-register mode always is a user mode access,
the code to inspect the access-registers can be removed. The second
change is to use a different test to check for no-execute fault.
The third change is to pass the translation exception identification
as parameter, in theory the trans_exc_code in the lowcore could have
been overwritten by the time the call to check_space from do_no_context
is done.

Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
---

arch/s390/mm/fault.c | 99 +++++++++++++++++++++++----------------------------
1 file changed, 45 insertions(+), 54 deletions(-)

Index: quilt-2.6/arch/s390/mm/fault.c
===================================================================
--- quilt-2.6.orig/arch/s390/mm/fault.c 2009-11-13 15:48:32.000000000 +0100
+++ quilt-2.6/arch/s390/mm/fault.c 2009-11-13 16:08:12.000000000 +0100
@@ -100,39 +100,28 @@

/*
* Returns the address space associated with the fault.
- * Returns 0 for kernel space, 1 for user space and
- * 2 for code execution in user space with noexec=on.
+ * Returns 0 for kernel space and 1 for user space.
*/
-static inline int check_space(struct task_struct *tsk)
+static inline int user_space_fault(unsigned long trans_exc_code)
{
/*
- * The lowest two bits of S390_lowcore.trans_exc_code
- * indicate which paging table was used.
+ * The lowest two bits of the translation exception
+ * identification indicate which paging table was used.
*/
- int desc = S390_lowcore.trans_exc_code & 3;
-
- if (desc == 3) /* Home Segment Table Descriptor */
- return switch_amode == 0;
- if (desc == 2) /* Secondary Segment Table Descriptor */
- return tsk->thread.mm_segment.ar4;
-#ifdef CONFIG_S390_SWITCH_AMODE
- if (unlikely(desc == 1)) { /* STD determined via access register */
- /* %a0 always indicates primary space. */
- if (S390_lowcore.exc_access_id != 0) {
- save_access_regs(tsk->thread.acrs);
- /*
- * An alet of 0 indicates primary space.
- * An alet of 1 indicates secondary space.
- * Any other alet values generate an
- * alen-translation exception.
- */
- if (tsk->thread.acrs[S390_lowcore.exc_access_id])
- return tsk->thread.mm_segment.ar4;
- }
- }
-#endif
- /* Primary Segment Table Descriptor */
- return switch_amode << s390_noexec;
+ trans_exc_code &= 3;
+ if (trans_exc_code == 2)
+ /* Access via secondary space, set_fs setting decides */
+ return current->thread.mm_segment.ar4;
+ if (!switch_amode)
+ /* User space if the access has been done via home space. */
+ return trans_exc_code == 3;
+ /*
+ * If the user space is not the home space the kernel runs in home
+ * space. Access via secondary space has already been covered,
+ * access via primary space or access register is from user space
+ * and access via home space is from the kernel.
+ */
+ return trans_exc_code != 3;
}

/*
@@ -162,9 +151,10 @@
}

static void do_no_context(struct pt_regs *regs, unsigned long error_code,
- unsigned long address)
+ unsigned long trans_exc_code)
{
const struct exception_table_entry *fixup;
+ unsigned long address;

/* Are we prepared to handle this kernel fault? */
fixup = search_exception_tables(regs->psw.addr & __FIXUP_MASK);
@@ -177,7 +167,8 @@
* Oops. The kernel tried to access some bad page. We'll have to
* terminate things with extreme prejudice.
*/
- if (check_space(current) == 0)
+ address = trans_exc_code & __FAIL_ADDR_MASK;
+ if (user_space_fault(trans_exc_code) == 0)
printk(KERN_ALERT "Unable to handle kernel pointer dereference"
" at virtual kernel address %p\n", (void *)address);
else
@@ -188,7 +179,8 @@
do_exit(SIGKILL);
}

-static void do_low_address(struct pt_regs *regs, unsigned long error_code)
+static void do_low_address(struct pt_regs *regs, unsigned long error_code,
+ unsigned long trans_exc_code)
{
/* Low-address protection hit in kernel mode means
NULL pointer write access in kernel mode. */
@@ -198,11 +190,11 @@
do_exit(SIGKILL);
}

- do_no_context(regs, error_code, 0);
+ do_no_context(regs, error_code, trans_exc_code);
}

static void do_sigbus(struct pt_regs *regs, unsigned long error_code,
- unsigned long address)
+ unsigned long trans_exc_code)
{
struct task_struct *tsk = current;
struct mm_struct *mm = tsk->mm;
@@ -212,13 +204,13 @@
* Send a sigbus, regardless of whether we were in kernel
* or user mode.
*/
- tsk->thread.prot_addr = address;
+ tsk->thread.prot_addr = trans_exc_code & __FAIL_ADDR_MASK;
tsk->thread.trap_no = error_code;
force_sig(SIGBUS, tsk);

/* Kernel mode? Handle exceptions or die */
if (!(regs->psw.mask & PSW_MASK_PSTATE))
- do_no_context(regs, error_code, address);
+ do_no_context(regs, error_code, trans_exc_code);
}

#ifdef CONFIG_S390_EXEC_PROTECT
@@ -272,13 +264,13 @@
* 3b Region third trans. -> Not present (nullification)
*/
static inline void
-do_exception(struct pt_regs *regs, unsigned long error_code, int write)
+do_exception(struct pt_regs *regs, unsigned long error_code, int write,
+ unsigned long trans_exc_code)
{
struct task_struct *tsk;
struct mm_struct *mm;
struct vm_area_struct *vma;
unsigned long address;
- int space;
int si_code;
int fault;

@@ -288,18 +280,15 @@
tsk = current;
mm = tsk->mm;

- /* get the failing address and the affected space */
- address = S390_lowcore.trans_exc_code & __FAIL_ADDR_MASK;
- space = check_space(tsk);
-
/*
* Verify that the fault happened in user space, that
* we are not in an interrupt and that there is a
* user context.
*/
- if (unlikely(space == 0 || in_atomic() || !mm))
+ if (unlikely(!user_space_fault(trans_exc_code) || in_atomic() || !mm))
goto no_context;

+ address = trans_exc_code & __FAIL_ADDR_MASK;
/*
* When we get here, the fault happened in the current
* task's user address space, so we can switch on the
@@ -315,7 +304,8 @@
goto bad_area;

#ifdef CONFIG_S390_EXEC_PROTECT
- if (unlikely((space == 2) && !(vma->vm_flags & VM_EXEC)))
+ if (unlikely((regs->psw.mask & PSW_MASK_ASC) == PSW_ASC_SECONDARY &&
+ (trans_exc_code & 3) == 0 && !(vma->vm_flags & VM_EXEC)))
if (!signal_return(mm, regs, address, error_code))
/*
* signal_return() has done an up_read(&mm->mmap_sem)
@@ -397,12 +387,14 @@
}

no_context:
- do_no_context(regs, error_code, address);
+ do_no_context(regs, error_code, trans_exc_code);
}

void __kprobes do_protection_exception(struct pt_regs *regs,
long error_code)
{
+ unsigned long trans_exc_code = S390_lowcore.trans_exc_code;
+
/* Protection exception is supressing, decrement psw address. */
regs->psw.addr -= (error_code >> 16);
/*
@@ -410,31 +402,30 @@
* as a special case because the translation exception code
* field is not guaranteed to contain valid data in this case.
*/
- if (unlikely(!(S390_lowcore.trans_exc_code & 4))) {
- do_low_address(regs, error_code);
+ if (unlikely(!(trans_exc_code & 4))) {
+ do_low_address(regs, error_code, trans_exc_code);
return;
}
- do_exception(regs, 4, 1);
+ do_exception(regs, 4, 1, trans_exc_code);
}

void __kprobes do_dat_exception(struct pt_regs *regs, long error_code)
{
- do_exception(regs, error_code & 0xff, 0);
+ do_exception(regs, error_code & 0xff, 0, S390_lowcore.trans_exc_code);
}

#ifdef CONFIG_64BIT
void __kprobes do_asce_exception(struct pt_regs *regs, unsigned long error_code)
{
+ unsigned long trans_exc_code = S390_lowcore.trans_exc_code;
struct mm_struct *mm;
struct vm_area_struct *vma;
unsigned long address;
- int space;

mm = current->mm;
- address = S390_lowcore.trans_exc_code & __FAIL_ADDR_MASK;
- space = check_space(current);
+ address = trans_exc_code & __FAIL_ADDR_MASK;

- if (unlikely(space == 0 || in_atomic() || !mm))
+ if (unlikely(!user_space_fault(trans_exc_code) || in_atomic() || !mm))
goto no_context;

local_irq_enable();
@@ -457,7 +448,7 @@
}

no_context:
- do_no_context(regs, error_code, address);
+ do_no_context(regs, error_code, trans_exc_code);
}
#endif