Re: PowerPC paxtest results w/ gcc-4.1

["Albert Cahalan" <acahalan@gmail.com>]

On 8/12/06, Paul Mackerras <paulus@samba.org> wrote:
> Of course, that won't make all that much difference on your Cube,
> because the G4 CPU doesn't have hardware support for non-executable
> pages (any readable page is executable).

I now have an evil grin, and a kernel that prevents
execution from the stack. It passes that one part
of paxtest now.

If the -msecure-plt actually did something (it's a nop
according to md5sum) and the executable mappings
didn't share with other ones, I'd have it all protected.

Signed-off-by: Albert Cahalan

---------

--- linux-2.6.17-rc5/arch/powerpc/kernel/head_32.S      2006-05-24
21:50:17.000000000 -0400
+++ linux-17rc5-secure/arch/powerpc/kernel/head_32.S    2006-08-13
10:48:38.000000000 -0400
@@ -1182,7 +1182,7 @@
 _GLOBAL(set_context)
        mulli   r3,r3,897       /* multiply context by skew factor */
        rlwinm  r3,r3,4,8,27    /* VSID = (context & 0xfffff) << 4 */
-       addis   r3,r3,0x6000    /* Set Ks, Ku bits */
+       addis   r3,r3,0x7000    /* Set Ks, Ku, N bits */
        li      r0,NUM_USER_SEGMENTS
        mtctr   r0

--- linux-2.6.17-rc5/arch/powerpc/mm/fault.c    2006-05-24
21:50:17.000000000 -0400
+++ linux-17rc5-secure/arch/powerpc/mm/fault.c  2006-08-13
19:17:22.000000000 -0400
@@ -134,8 +134,8 @@
         * bits we are interested in.  But there are some bits which
         * indicate errors in DSISR but can validly be set in SRR1.
         */
-       if (trap == 0x400)
-               error_code &= 0x48200000;
+       if (is_exec)
+               error_code &= 0x58200000;
        else
                is_write = error_code & DSISR_ISSTORE;
 #else
@@ -242,7 +242,7 @@
 good_area:
        code = SEGV_ACCERR;
 #if defined(CONFIG_6xx)
-       if (error_code & 0x95700000)
+       if (error_code & 0x85700000)
                /* an error such as lwarx to I/O controller space,
                   address matching DABR, eciwx, etc. */
                goto bad_area;
@@ -258,12 +258,24 @@
 #endif /* CONFIG_8xx */

        if (is_exec) {
+               if (!(vma->vm_flags & VM_EXEC)) {
+#if 0
+                       static __typeof__(jiffies) oldjif;
+                       static int count;
+                       if(count++ < 5)
+                       printk(KERN_CRIT "fuckup @ %08lx with trap
0x%x code %08lx by %s\n",
+                               address, trap, error_code, current->comm);
+                       if(jiffies/(HZ*15) != oldjif/(HZ*15)) {
+                               oldjif = jiffies;
+                               count = 0;
+                       }
+#endif
+                       goto bad_area;
+               }
 #ifdef CONFIG_PPC64
                /* protection fault */
                if (error_code & DSISR_PROTFAULT)
                        goto bad_area;
-               if (!(vma->vm_flags & VM_EXEC))
-                       goto bad_area;
 #endif
 #if defined(CONFIG_4xx) || defined(CONFIG_BOOKE)
                pte_t *ptep;
@@ -291,6 +303,27 @@
                        pte_unmap_unlock(ptep, ptl);
                }
 #endif
+#if !defined(CONFIG_4xx) && !defined(CONFIG_BOOKE) && !defined(CONFIG_PPC64)
+               if (!(error_code & 0x10000000))
+                       goto survive;
+               /* It was an ISI exception with SRR1 bit 3 set.
+                * We have no-execute bits in the 256 MiB segments.
+                * We sometimes take faults to turn the bits on.
+                * Faults happen when the user executes from guarded mem,
+                * no-execute segment, or (extinct) direct-store segment.
+                * The segment-related faults happen first. */
+               unsigned segreg;
+               __asm__ __volatile__("mfsrin %0,%1":"=r"(segreg):"r"(address));
+               /* if current segment is no-execute but not direct-store */
+               if (segreg>>28==7) {
+                       /* clear the N bit to make it executable */
+                       segreg &= 0x6fffffff;
+                       __asm__ __volatile__("mtsrin
%0,%1"::"r"(segreg),"r"(address));
+                       /* TODO: as this one goes executable, make
other segments not */
+                       up_read(&mm->mmap_sem);
+                       return 0;
+               }
+#endif
        /* a write */
        } else if (is_write) {
                if (!(vma->vm_flags & VM_WRITE))
@@ -300,7 +333,7 @@
                /* protection fault */
                if (error_code & 0x08000000)
                        goto bad_area;
-               if (!(vma->vm_flags & (VM_READ | VM_EXEC)))
+               if (!(vma->vm_flags & (VM_READ | VM_EXEC))) /* VM_EXEC
wrong for ppc32? */
                        goto bad_area;
        }

--- linux-2.6.17-rc5/include/asm-powerpc/page.h 2006-05-24
21:50:17.000000000 -0400
+++ linux-17rc5-secure/include/asm-powerpc/page.h       2006-08-13
11:58:25.000000000 -0400
@@ -90,6 +90,9 @@
 #define VM_DATA_DEFAULT_FLAGS64        (VM_READ | VM_WRITE | \
                                 VM_MAYREAD | VM_MAYWRITE | VM_MAYEXEC)

+#define VM_STACK_DEFAULT_FLAGS (VM_READ | VM_WRITE | \
+                                VM_MAYREAD | VM_MAYWRITE | VM_MAYEXEC)
+
 #ifdef __powerpc64__
 #include <asm/page_64.h>
 #else