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authorJason Baron <jbaron@redhat.com>2006-09-29 04:58:58 -0400
committerLinus Torvalds <torvalds@g5.osdl.org>2006-09-29 12:18:05 -0400
commitdf67b3daea602728b51325a4debaeeb912ee51d1 (patch)
tree22181d324d541a27b037673cf1315827900e998c /arch
parent15a67dd8ccf696392176c95a08234a8b8ee59005 (diff)
[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 f0943d160ffe..a5b33ff3924e 100644
--- a/arch/arm/mm/fault.c
+++ b/arch/arm/mm/fault.c
@@ -171,7 +171,7 @@ good_area:
171 if (fsr & (1 << 11)) /* write? */ 171 if (fsr & (1 << 11)) /* write? */
172 mask = VM_WRITE; 172 mask = VM_WRITE;
173 else 173 else
174 mask = VM_READ|VM_EXEC; 174 mask = VM_READ|VM_EXEC|VM_WRITE;
175 175
176 fault = VM_FAULT_BADACCESS; 176 fault = VM_FAULT_BADACCESS;
177 if (!(vma->vm_flags & mask)) 177 if (!(vma->vm_flags & mask))
diff --git a/arch/arm26/mm/fault.c b/arch/arm26/mm/fault.c
index 761938b56679..a7c4cc922095 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,
155 */ 155 */
156good_area: 156good_area:
157 if (READ_FAULT(fsr)) /* read? */ 157 if (READ_FAULT(fsr)) /* read? */
158 mask = VM_READ|VM_EXEC; 158 mask = VM_READ|VM_EXEC|VM_WRITE;
159 else 159 else
160 mask = VM_WRITE; 160 mask = VM_WRITE;
161 161
diff --git a/arch/i386/mm/fault.c b/arch/i386/mm/fault.c
index 5e17a3f43b41..50d8617391dd 100644
--- a/arch/i386/mm/fault.c
+++ b/arch/i386/mm/fault.c
@@ -440,7 +440,7 @@ good_area:
440 case 1: /* read, present */ 440 case 1: /* read, present */
441 goto bad_area; 441 goto bad_area;
442 case 0: /* read, not present */ 442 case 0: /* read, not present */
443 if (!(vma->vm_flags & (VM_READ | VM_EXEC))) 443 if (!(vma->vm_flags & (VM_READ | VM_EXEC | VM_WRITE)))
444 goto bad_area; 444 goto bad_area;
445 } 445 }
446 446
diff --git a/arch/ia64/mm/fault.c b/arch/ia64/mm/fault.c
index 14ef7cceb208..d8b1b4ac7f26 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
146# error File is out of sync with <linux/mm.h>. Please update. 146# error File is out of sync with <linux/mm.h>. Please update.
147# endif 147# endif
148 148
149 if (((isr >> IA64_ISR_R_BIT) & 1UL) && (!(vma->vm_flags & (VM_READ | VM_WRITE))))
150 goto bad_area;
151
149 mask = ( (((isr >> IA64_ISR_X_BIT) & 1UL) << VM_EXEC_BIT) 152 mask = ( (((isr >> IA64_ISR_X_BIT) & 1UL) << VM_EXEC_BIT)
150 | (((isr >> IA64_ISR_W_BIT) & 1UL) << VM_WRITE_BIT) 153 | (((isr >> IA64_ISR_W_BIT) & 1UL) << VM_WRITE_BIT));
151 | (((isr >> IA64_ISR_R_BIT) & 1UL) << VM_READ_BIT));
152 154
153 if ((vma->vm_flags & mask) != mask) 155 if ((vma->vm_flags & mask) != mask)
154 goto bad_area; 156 goto bad_area;
diff --git a/arch/m68k/mm/fault.c b/arch/m68k/mm/fault.c
index aec15270d334..5e2d87c10c87 100644
--- a/arch/m68k/mm/fault.c
+++ b/arch/m68k/mm/fault.c
@@ -144,7 +144,7 @@ good_area:
144 case 1: /* read, present */ 144 case 1: /* read, present */
145 goto acc_err; 145 goto acc_err;
146 case 0: /* read, not present */ 146 case 0: /* read, not present */
147 if (!(vma->vm_flags & (VM_READ | VM_EXEC))) 147 if (!(vma->vm_flags & (VM_READ | VM_EXEC | VM_WRITE)))
148 goto acc_err; 148 goto acc_err;
149 } 149 }
150 150
diff --git a/arch/powerpc/mm/fault.c b/arch/powerpc/mm/fault.c
index 78a0d59903ee..77953f41d754 100644
--- a/arch/powerpc/mm/fault.c
+++ b/arch/powerpc/mm/fault.c
@@ -333,7 +333,7 @@ good_area:
333 /* protection fault */ 333 /* protection fault */
334 if (error_code & 0x08000000) 334 if (error_code & 0x08000000)
335 goto bad_area; 335 goto bad_area;
336 if (!(vma->vm_flags & (VM_READ | VM_EXEC))) 336 if (!(vma->vm_flags & (VM_READ | VM_EXEC | VM_WRITE)))
337 goto bad_area; 337 goto bad_area;
338 } 338 }
339 339
diff --git a/arch/ppc/mm/fault.c b/arch/ppc/mm/fault.c
index 5cdfb71fcb07..bc776beb3136 100644
--- a/arch/ppc/mm/fault.c
+++ b/arch/ppc/mm/fault.c
@@ -239,7 +239,7 @@ good_area:
239 /* protection fault */ 239 /* protection fault */
240 if (error_code & 0x08000000) 240 if (error_code & 0x08000000)
241 goto bad_area; 241 goto bad_area;
242 if (!(vma->vm_flags & (VM_READ | VM_EXEC))) 242 if (!(vma->vm_flags & (VM_READ | VM_EXEC | VM_WRITE)))
243 goto bad_area; 243 goto bad_area;
244 } 244 }
245 245
diff --git a/arch/sh/mm/fault.c b/arch/sh/mm/fault.c
index c69fd603226a..507f28914706 100644
--- a/arch/sh/mm/fault.c
+++ b/arch/sh/mm/fault.c
@@ -69,7 +69,7 @@ good_area:
69 if (!(vma->vm_flags & VM_WRITE)) 69 if (!(vma->vm_flags & VM_WRITE))
70 goto bad_area; 70 goto bad_area;
71 } else { 71 } else {
72 if (!(vma->vm_flags & (VM_READ | VM_EXEC))) 72 if (!(vma->vm_flags & (VM_READ | VM_EXEC | VM_WRITE)))
73 goto bad_area; 73 goto bad_area;
74 } 74 }
75 75
diff --git a/arch/x86_64/mm/fault.c b/arch/x86_64/mm/fault.c
index 1a17b0733ab5..9ba54cc2b5f6 100644
--- a/arch/x86_64/mm/fault.c
+++ b/arch/x86_64/mm/fault.c
@@ -464,7 +464,7 @@ good_area:
464 case PF_PROT: /* read, present */ 464 case PF_PROT: /* read, present */
465 goto bad_area; 465 goto bad_area;
466 case 0: /* read, not present */ 466 case 0: /* read, not present */
467 if (!(vma->vm_flags & (VM_READ | VM_EXEC))) 467 if (!(vma->vm_flags & (VM_READ | VM_EXEC | VM_WRITE)))
468 goto bad_area; 468 goto bad_area;
469 } 469 }
470 470