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authorJason Baron <jbaron@redhat.com>2006-09-29 01:58:58 -0700
committerLinus Torvalds <torvalds@g5.osdl.org>2006-09-29 09:18:05 -0700
commitdf67b3daea602728b51325a4debaeeb912ee51d1 (patch)
tree22181d324d541a27b037673cf1315827900e998c /arch
parent15a67dd8ccf696392176c95a08234a8b8ee59005 (diff)
downloadlinaro-lsk-df67b3daea602728b51325a4debaeeb912ee51d1.tar.gz
[PATCH] make PROT_WRITE imply PROT_READ
Make PROT_WRITE imply PROT_READ for a number of architectures which don't support write only in hardware. While looking at this, I noticed that some architectures which do not support write only mappings already take the exact same approach. For example, in arch/alpha/mm/fault.c: " if (cause < 0) { if (!(vma->vm_flags & VM_EXEC)) goto bad_area; } else if (!cause) { /* Allow reads even for write-only mappings */ if (!(vma->vm_flags & (VM_READ | VM_WRITE))) goto bad_area; } else { if (!(vma->vm_flags & VM_WRITE)) goto bad_area; } " Thus, this patch brings other architectures which do not support write only mappings in-line and consistent with the rest. I've verified the patch on ia64, x86_64 and x86. Additional discussion: Several architectures, including x86, can not support write-only mappings. The pte for x86 reserves a single bit for protection and its two states are read only or read/write. Thus, write only is not supported in h/w. Currently, if i 'mmap' a page write-only, the first read attempt on that page creates a page fault and will SEGV. That check is enforced in arch/blah/mm/fault.c. However, if i first write that page it will fault in and the pte will be set to read/write. Thus, any subsequent reads to the page will succeed. It is this inconsistency in behavior that this patch is attempting to address. Furthermore, if the page is swapped out, and then brought back the first read will also cause a SEGV. Thus, any arbitrary read on a page can potentially result in a SEGV. According to the SuSv3 spec, "if the application requests only PROT_WRITE, the implementation may also allow read access." Also as mentioned, some archtectures, such as alpha, shown above already take the approach that i am suggesting. The counter-argument to this raised by Arjan, is that the kernel is enforcing the write only mapping the best it can given the h/w limitations. This is true, however Alan Cox, and myself would argue that the inconsitency in behavior, that is applications can sometimes work/sometimes fails is highly undesireable. If you read through the thread, i think people, came to an agreement on the last patch i posted, as nobody has objected to it... Signed-off-by: Jason Baron <jbaron@redhat.com> Cc: Russell King <rmk@arm.linux.org.uk> Cc: "Luck, Tony" <tony.luck@intel.com> Cc: Hugh Dickins <hugh@veritas.com> Cc: Roman Zippel <zippel@linux-m68k.org> Cc: Geert Uytterhoeven <geert@linux-m68k.org> Cc: Paul Mackerras <paulus@samba.org> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org> Acked-by: Andi Kleen <ak@muc.de> Acked-by: Alan Cox <alan@lxorguk.ukuu.org.uk> Cc: Arjan van de Ven <arjan@linux.intel.com> Acked-by: Paul Mundt <lethal@linux-sh.org> Cc: Kazumoto Kojima <kkojima@rr.iij4u.or.jp> Cc: Ian Molton <spyro@f2s.com> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
Diffstat (limited to 'arch')
-rw-r--r--arch/arm/mm/fault.c2
-rw-r--r--arch/arm26/mm/fault.c2
-rw-r--r--arch/i386/mm/fault.c2
-rw-r--r--arch/ia64/mm/fault.c6
-rw-r--r--arch/m68k/mm/fault.c2
-rw-r--r--arch/powerpc/mm/fault.c2
-rw-r--r--arch/ppc/mm/fault.c2
-rw-r--r--arch/sh/mm/fault.c2
-rw-r--r--arch/x86_64/mm/fault.c2
9 files changed, 12 insertions, 10 deletions
diff --git a/arch/arm/mm/fault.c b/arch/arm/mm/fault.c
index f0943d160ff..a5b33ff3924 100644
--- a/arch/arm/mm/fault.c
+++ b/arch/arm/mm/fault.c
@@ -171,7 +171,7 @@ good_area:
if (fsr & (1 << 11)) /* write? */
mask = VM_WRITE;
else
- mask = VM_READ|VM_EXEC;
+ mask = VM_READ|VM_EXEC|VM_WRITE;
fault = VM_FAULT_BADACCESS;
if (!(vma->vm_flags & mask))
diff --git a/arch/arm26/mm/fault.c b/arch/arm26/mm/fault.c
index 761938b5667..a7c4cc92209 100644
--- a/arch/arm26/mm/fault.c
+++ b/arch/arm26/mm/fault.c
@@ -155,7 +155,7 @@ __do_page_fault(struct mm_struct *mm, unsigned long addr, unsigned int fsr,
*/
good_area:
if (READ_FAULT(fsr)) /* read? */
- mask = VM_READ|VM_EXEC;
+ mask = VM_READ|VM_EXEC|VM_WRITE;
else
mask = VM_WRITE;
diff --git a/arch/i386/mm/fault.c b/arch/i386/mm/fault.c
index 5e17a3f43b4..50d8617391d 100644
--- a/arch/i386/mm/fault.c
+++ b/arch/i386/mm/fault.c
@@ -440,7 +440,7 @@ good_area:
case 1: /* read, present */
goto bad_area;
case 0: /* read, not present */
- if (!(vma->vm_flags & (VM_READ | VM_EXEC)))
+ if (!(vma->vm_flags & (VM_READ | VM_EXEC | VM_WRITE)))
goto bad_area;
}
diff --git a/arch/ia64/mm/fault.c b/arch/ia64/mm/fault.c
index 14ef7cceb20..d8b1b4ac7f2 100644
--- a/arch/ia64/mm/fault.c
+++ b/arch/ia64/mm/fault.c
@@ -146,9 +146,11 @@ ia64_do_page_fault (unsigned long address, unsigned long isr, struct pt_regs *re
# error File is out of sync with <linux/mm.h>. Please update.
# endif
+ if (((isr >> IA64_ISR_R_BIT) & 1UL) && (!(vma->vm_flags & (VM_READ | VM_WRITE))))
+ goto bad_area;
+
mask = ( (((isr >> IA64_ISR_X_BIT) & 1UL) << VM_EXEC_BIT)
- | (((isr >> IA64_ISR_W_BIT) & 1UL) << VM_WRITE_BIT)
- | (((isr >> IA64_ISR_R_BIT) & 1UL) << VM_READ_BIT));
+ | (((isr >> IA64_ISR_W_BIT) & 1UL) << VM_WRITE_BIT));
if ((vma->vm_flags & mask) != mask)
goto bad_area;
diff --git a/arch/m68k/mm/fault.c b/arch/m68k/mm/fault.c
index aec15270d33..5e2d87c10c8 100644
--- a/arch/m68k/mm/fault.c
+++ b/arch/m68k/mm/fault.c
@@ -144,7 +144,7 @@ good_area:
case 1: /* read, present */
goto acc_err;
case 0: /* read, not present */
- if (!(vma->vm_flags & (VM_READ | VM_EXEC)))
+ if (!(vma->vm_flags & (VM_READ | VM_EXEC | VM_WRITE)))
goto acc_err;
}
diff --git a/arch/powerpc/mm/fault.c b/arch/powerpc/mm/fault.c
index 78a0d59903e..77953f41d75 100644
--- a/arch/powerpc/mm/fault.c
+++ b/arch/powerpc/mm/fault.c
@@ -333,7 +333,7 @@ good_area:
/* 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_WRITE)))
goto bad_area;
}
diff --git a/arch/ppc/mm/fault.c b/arch/ppc/mm/fault.c
index 5cdfb71fcb0..bc776beb313 100644
--- a/arch/ppc/mm/fault.c
+++ b/arch/ppc/mm/fault.c
@@ -239,7 +239,7 @@ good_area:
/* 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_WRITE)))
goto bad_area;
}
diff --git a/arch/sh/mm/fault.c b/arch/sh/mm/fault.c
index c69fd603226..507f2891470 100644
--- a/arch/sh/mm/fault.c
+++ b/arch/sh/mm/fault.c
@@ -69,7 +69,7 @@ good_area:
if (!(vma->vm_flags & VM_WRITE))
goto bad_area;
} else {
- if (!(vma->vm_flags & (VM_READ | VM_EXEC)))
+ if (!(vma->vm_flags & (VM_READ | VM_EXEC | VM_WRITE)))
goto bad_area;
}
diff --git a/arch/x86_64/mm/fault.c b/arch/x86_64/mm/fault.c
index 1a17b0733ab..9ba54cc2b5f 100644
--- a/arch/x86_64/mm/fault.c
+++ b/arch/x86_64/mm/fault.c
@@ -464,7 +464,7 @@ good_area:
case PF_PROT: /* read, present */
goto bad_area;
case 0: /* read, not present */
- if (!(vma->vm_flags & (VM_READ | VM_EXEC)))
+ if (!(vma->vm_flags & (VM_READ | VM_EXEC | VM_WRITE)))
goto bad_area;
}