coredump: remove VM_ALWAYSDUMP flag

The motivation for this patchset was that I was looking at a way for a
qemu-kvm process, to exclude the guest memory from its core dump, which
can be quite large.  There are already a number of filter flags in
/proc/<pid>/coredump_filter, however, these allow one to specify 'types'
of kernel memory, not specific address ranges (which is needed in this
case).

Since there are no more vma flags available, the first patch eliminates
the need for the 'VM_ALWAYSDUMP' flag.  The flag is used internally by
the kernel to mark vdso and vsyscall pages.  However, it is simple
enough to check if a vma covers a vdso or vsyscall page without the need
for this flag.

The second patch then replaces the 'VM_ALWAYSDUMP' flag with a new
'VM_NODUMP' flag, which can be set by userspace using new madvise flags:
'MADV_DONTDUMP', and unset via 'MADV_DODUMP'.  The core dump filters
continue to work the same as before unless 'MADV_DONTDUMP' is set on the
region.

The qemu code which implements this features is at:

  http://people.redhat.com/~jbaron/qemu-dump/qemu-dump.patch

In my testing the qemu core dump shrunk from 383MB -> 13MB with this
patch.

I also believe that the 'MADV_DONTDUMP' flag might be useful for
security sensitive apps, which might want to select which areas are
dumped.

This patch:

The VM_ALWAYSDUMP flag is currently used by the coredump code to
indicate that a vma is part of a vsyscall or vdso section.  However, we
can determine if a vma is in one these sections by checking it against
the gate_vma and checking for a non-NULL return value from
arch_vma_name().  Thus, freeing a valuable vma bit.

Signed-off-by: Jason Baron <jbaron@redhat.com>
Acked-by: Roland McGrath <roland@hack.frob.com>
Cc: Chris Metcalf <cmetcalf@tilera.com>
Cc: Avi Kivity <avi@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

15 files changed, 40 insertions, 69 deletions

diff --git a/arch/arm/kernel/process.c b/arch/arm/kernel/process.c
index c2ae3cd331f..219e4efee1a 100644
--- a/arch/arm/kernel/process.c
+++ b/arch/arm/kernel/process.c
@@ -533,8 +533,7 @@ int vectors_user_mapping(void)
 	struct mm_struct *mm = current->mm;
 	return install_special_mapping(mm, 0xffff0000, PAGE_SIZE,
 				       VM_READ | VM_EXEC |
-				       VM_MAYREAD | VM_MAYEXEC |
-				       VM_ALWAYSDUMP | VM_RESERVED,
+				       VM_MAYREAD | VM_MAYEXEC | VM_RESERVED,
 				       NULL);
 }
 
diff --git a/arch/hexagon/kernel/vdso.c b/arch/hexagon/kernel/vdso.c
index 16277c33308..f212a453b52 100644
--- a/arch/hexagon/kernel/vdso.c
+++ b/arch/hexagon/kernel/vdso.c
@@ -78,8 +78,7 @@ int arch_setup_additional_pages(struct linux_binprm *bprm, int uses_interp)
 	/* MAYWRITE to allow gdb to COW and set breakpoints. */
 	ret = install_special_mapping(mm, vdso_base, PAGE_SIZE,
 				      VM_READ|VM_EXEC|
-				      VM_MAYREAD|VM_MAYWRITE|VM_MAYEXEC|
-				      VM_ALWAYSDUMP,
+				      VM_MAYREAD|VM_MAYWRITE|VM_MAYEXEC,
 				      &vdso_page);
 
 	if (ret)
diff --git a/arch/mips/kernel/vdso.c b/arch/mips/kernel/vdso.c
index e5cdfd603f8..0f1af58b036 100644
--- a/arch/mips/kernel/vdso.c
+++ b/arch/mips/kernel/vdso.c
@@ -88,8 +88,7 @@ int arch_setup_additional_pages(struct linux_binprm *bprm, int uses_interp)
 
 	ret = install_special_mapping(mm, addr, PAGE_SIZE,
 				      VM_READ|VM_EXEC|
-				      VM_MAYREAD|VM_MAYWRITE|VM_MAYEXEC|
-				      VM_ALWAYSDUMP,
+				      VM_MAYREAD|VM_MAYWRITE|VM_MAYEXEC,
 				      &vdso_page);
 
 	if (ret)
diff --git a/arch/powerpc/kernel/vdso.c b/arch/powerpc/kernel/vdso.c
index 7d14bb697d4..d36ee1055f8 100644
--- a/arch/powerpc/kernel/vdso.c
+++ b/arch/powerpc/kernel/vdso.c
@@ -263,17 +263,11 @@ int arch_setup_additional_pages(struct linux_binprm *bprm, int uses_interp)
 	 * the "data" page of the vDSO or you'll stop getting kernel updates
 	 * and your nice userland gettimeofday will be totally dead.
 	 * It's fine to use that for setting breakpoints in the vDSO code
-	 * pages though
-	 *
-	 * Make sure the vDSO gets into every core dump.
-	 * Dumping its contents makes post-mortem fully interpretable later
-	 * without matching up the same kernel and hardware config to see
-	 * what PC values meant.
+	 * pages though.
 	 */
 	rc = install_special_mapping(mm, vdso_base, vdso_pages << PAGE_SHIFT,
 				     VM_READ|VM_EXEC|
-				     VM_MAYREAD|VM_MAYWRITE|VM_MAYEXEC|
-				     VM_ALWAYSDUMP,
+				     VM_MAYREAD|VM_MAYWRITE|VM_MAYEXEC,
 				     vdso_pagelist);
 	if (rc) {
 		current->mm->context.vdso_base = 0;
diff --git a/arch/s390/kernel/vdso.c b/arch/s390/kernel/vdso.c
index e704a9965f9..9c80138206b 100644
--- a/arch/s390/kernel/vdso.c
+++ b/arch/s390/kernel/vdso.c
@@ -241,17 +241,11 @@ int arch_setup_additional_pages(struct linux_binprm *bprm, int uses_interp)
 	 * on the "data" page of the vDSO or you'll stop getting kernel
 	 * updates and your nice userland gettimeofday will be totally dead.
 	 * It's fine to use that for setting breakpoints in the vDSO code
-	 * pages though
-	 *
-	 * Make sure the vDSO gets into every core dump.
-	 * Dumping its contents makes post-mortem fully interpretable later
-	 * without matching up the same kernel and hardware config to see
-	 * what PC values meant.
+	 * pages though.
 	 */
 	rc = install_special_mapping(mm, vdso_base, vdso_pages << PAGE_SHIFT,
 				     VM_READ|VM_EXEC|
-				     VM_MAYREAD|VM_MAYWRITE|VM_MAYEXEC|
-				     VM_ALWAYSDUMP,
+				     VM_MAYREAD|VM_MAYWRITE|VM_MAYEXEC,
 				     vdso_pagelist);
 	if (rc)
 		current->mm->context.vdso_base = 0;
diff --git a/arch/sh/kernel/vsyscall/vsyscall.c b/arch/sh/kernel/vsyscall/vsyscall.c
index 1d6d51a1ce7..5ca579720a0 100644
--- a/arch/sh/kernel/vsyscall/vsyscall.c
+++ b/arch/sh/kernel/vsyscall/vsyscall.c
@@ -73,8 +73,7 @@ int arch_setup_additional_pages(struct linux_binprm *bprm, int uses_interp)
 
 	ret = install_special_mapping(mm, addr, PAGE_SIZE,
 				      VM_READ | VM_EXEC |
-				      VM_MAYREAD | VM_MAYWRITE | VM_MAYEXEC |
-				      VM_ALWAYSDUMP,
+				      VM_MAYREAD | VM_MAYWRITE | VM_MAYEXEC,
 				      syscall_pages);
 	if (unlikely(ret))
 		goto up_fail;
diff --git a/arch/tile/mm/elf.c b/arch/tile/mm/elf.c
index 55e58e93bfc..1a00fb64fc8 100644
--- a/arch/tile/mm/elf.c
+++ b/arch/tile/mm/elf.c
@@ -117,17 +117,11 @@ int arch_setup_additional_pages(struct linux_binprm *bprm,
 
 	/*
 	 * MAYWRITE to allow gdb to COW and set breakpoints
-	 *
-	 * Make sure the vDSO gets into every core dump.  Dumping its
-	 * contents makes post-mortem fully interpretable later
-	 * without matching up the same kernel and hardware config to
-	 * see what PC values meant.
 	 */
 	vdso_base = VDSO_BASE;
 	retval = install_special_mapping(mm, vdso_base, PAGE_SIZE,
 					 VM_READ|VM_EXEC|
-					 VM_MAYREAD|VM_MAYWRITE|VM_MAYEXEC|
-					 VM_ALWAYSDUMP,
+					 VM_MAYREAD|VM_MAYWRITE|VM_MAYEXEC,
 					 vdso_pages);
 
 #ifndef __tilegx__
diff --git a/arch/unicore32/kernel/process.c b/arch/unicore32/kernel/process.c
index 52edc2b6287..432b4291f37 100644
--- a/arch/unicore32/kernel/process.c
+++ b/arch/unicore32/kernel/process.c
@@ -381,7 +381,7 @@ int vectors_user_mapping(void)
 	return install_special_mapping(mm, 0xffff0000, PAGE_SIZE,
 				       VM_READ | VM_EXEC |
 				       VM_MAYREAD | VM_MAYEXEC |
-				       VM_ALWAYSDUMP | VM_RESERVED,
+				       VM_RESERVED,
 				       NULL);
 }
 
diff --git a/arch/x86/um/mem_32.c b/arch/x86/um/mem_32.c
index 639900a6fde..f40281e5d6a 100644
--- a/arch/x86/um/mem_32.c
+++ b/arch/x86/um/mem_32.c
@@ -23,14 +23,6 @@ static int __init gate_vma_init(void)
 	gate_vma.vm_flags = VM_READ | VM_MAYREAD | VM_EXEC | VM_MAYEXEC;
 	gate_vma.vm_page_prot = __P101;
 
-	/*
-	 * Make sure the vDSO gets into every core dump.
-	 * Dumping its contents makes post-mortem fully interpretable later
-	 * without matching up the same kernel and hardware config to see
-	 * what PC values meant.
-	 */
-	gate_vma.vm_flags |= VM_ALWAYSDUMP;
-
 	return 0;
 }
 __initcall(gate_vma_init);
diff --git a/arch/x86/um/vdso/vma.c b/arch/x86/um/vdso/vma.c
index 91f4ec9a0a5..af91901babb 100644
--- a/arch/x86/um/vdso/vma.c
+++ b/arch/x86/um/vdso/vma.c
@@ -64,8 +64,7 @@ int arch_setup_additional_pages(struct linux_binprm *bprm, int uses_interp)
 
 	err = install_special_mapping(mm, um_vdso_addr, PAGE_SIZE,
 		VM_READ|VM_EXEC|
-		VM_MAYREAD|VM_MAYWRITE|VM_MAYEXEC|
-		VM_ALWAYSDUMP,
+		VM_MAYREAD|VM_MAYWRITE|VM_MAYEXEC,
 		vdsop);
 
 	up_write(&mm->mmap_sem);
diff --git a/arch/x86/vdso/vdso32-setup.c b/arch/x86/vdso/vdso32-setup.c
index 468d591dde3..a944020fa85 100644
--- a/arch/x86/vdso/vdso32-setup.c
+++ b/arch/x86/vdso/vdso32-setup.c
@@ -250,13 +250,7 @@ static int __init gate_vma_init(void)
 	gate_vma.vm_end = FIXADDR_USER_END;
 	gate_vma.vm_flags = VM_READ | VM_MAYREAD | VM_EXEC | VM_MAYEXEC;
 	gate_vma.vm_page_prot = __P101;
-	/*
-	 * Make sure the vDSO gets into every core dump.
-	 * Dumping its contents makes post-mortem fully interpretable later
-	 * without matching up the same kernel and hardware config to see
-	 * what PC values meant.
-	 */
-	gate_vma.vm_flags |= VM_ALWAYSDUMP;
+
 	return 0;
 }
 
@@ -343,17 +337,10 @@ int arch_setup_additional_pages(struct linux_binprm *bprm, int uses_interp)
 	if (compat_uses_vma || !compat) {
 		/*
 		 * MAYWRITE to allow gdb to COW and set breakpoints
-		 *
-		 * Make sure the vDSO gets into every core dump.
-		 * Dumping its contents makes post-mortem fully
-		 * interpretable later without matching up the same
-		 * kernel and hardware config to see what PC values
-		 * meant.
 		 */
 		ret = install_special_mapping(mm, addr, PAGE_SIZE,
 					      VM_READ|VM_EXEC|
-					      VM_MAYREAD|VM_MAYWRITE|VM_MAYEXEC|
-					      VM_ALWAYSDUMP,
+					      VM_MAYREAD|VM_MAYWRITE|VM_MAYEXEC,
 					      vdso32_pages);
 
 		if (ret)
diff --git a/arch/x86/vdso/vma.c b/arch/x86/vdso/vma.c
index 153407c35b7..17e18279649 100644
--- a/arch/x86/vdso/vma.c
+++ b/arch/x86/vdso/vma.c
@@ -124,8 +124,7 @@ int arch_setup_additional_pages(struct linux_binprm *bprm, int uses_interp)
 
 	ret = install_special_mapping(mm, addr, vdso_size,
 				      VM_READ|VM_EXEC|
-				      VM_MAYREAD|VM_MAYWRITE|VM_MAYEXEC|
-				      VM_ALWAYSDUMP,
+				      VM_MAYREAD|VM_MAYWRITE|VM_MAYEXEC,
 				      vdso_pages);
 	if (ret) {
 		current->mm->context.vdso = NULL;
diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c
index 81878b78c9d..b64be5b5ac2 100644
--- a/fs/binfmt_elf.c
+++ b/fs/binfmt_elf.c
@@ -1093,6 +1093,29 @@ out:
  */
 
 /*
+ * The purpose of always_dump_vma() is to make sure that special kernel mappings
+ * that are useful for post-mortem analysis are included in every core dump.
+ * In that way we ensure that the core dump is fully interpretable later
+ * without matching up the same kernel and hardware config to see what PC values
+ * meant. These special mappings include - vDSO, vsyscall, and other
+ * architecture specific mappings
+ */
+static bool always_dump_vma(struct vm_area_struct *vma)
+{
+	/* Any vsyscall mappings? */
+	if (vma == get_gate_vma(vma->vm_mm))
+		return true;
+	/*
+	 * arch_vma_name() returns non-NULL for special architecture mappings,
+	 * such as vDSO sections.
+	 */
+	if (arch_vma_name(vma))
+		return true;
+
+	return false;
+}
+
+/*
  * Decide what to dump of a segment, part, all or none.
  */
 static unsigned long vma_dump_size(struct vm_area_struct *vma,
@@ -1100,8 +1123,8 @@ static unsigned long vma_dump_size(struct vm_area_struct *vma,
 {
 #define FILTER(type)	(mm_flags & (1UL << MMF_DUMP_##type))
 
-	/* The vma can be set up to tell us the answer directly.  */
-	if (vma->vm_flags & VM_ALWAYSDUMP)
+	/* always dump the vdso and vsyscall sections */
+	if (always_dump_vma(vma))
 		goto whole;
 
 	/* Hugetlb memory check */
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 7330742e797..2de2ddba51d 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -111,7 +111,6 @@ extern unsigned int kobjsize(const void *objp);
 #define VM_HUGEPAGE	0x01000000	/* MADV_HUGEPAGE marked this vma */
 #endif
 #define VM_INSERTPAGE	0x02000000	/* The vma has had "vm_insert_page()" done on it */
-#define VM_ALWAYSDUMP	0x04000000	/* Always include in core dumps */
 
 #define VM_CAN_NONLINEAR 0x08000000	/* Has ->fault & does nonlinear pages */
 #define VM_MIXEDMAP	0x10000000	/* Can contain "struct page" and pure PFN pages */
diff --git a/mm/memory.c b/mm/memory.c
index 3416b6e018d..6105f475fa8 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -3623,13 +3623,7 @@ static int __init gate_vma_init(void)
 	gate_vma.vm_end = FIXADDR_USER_END;
 	gate_vma.vm_flags = VM_READ | VM_MAYREAD | VM_EXEC | VM_MAYEXEC;
 	gate_vma.vm_page_prot = __P101;
-	/*
-	 * Make sure the vDSO gets into every core dump.
-	 * Dumping its contents makes post-mortem fully interpretable later
-	 * without matching up the same kernel and hardware config to see
-	 * what PC values meant.
-	 */
-	gate_vma.vm_flags |= VM_ALWAYSDUMP;
+
 	return 0;
 }
 __initcall(gate_vma_init);