From 909af768e88867016f427264ae39d27a57b6a8ed Mon Sep 17 00:00:00 2001 From: Jason Baron Date: Fri, 23 Mar 2012 15:02:51 -0700 Subject: 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//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 Acked-by: Roland McGrath Cc: Chris Metcalf Cc: Avi Kivity Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- arch/mips/kernel/vdso.c | 3 +-- 1 file changed, 1 insertion(+), 2 deletions(-) (limited to 'arch/mips') diff --git a/arch/mips/kernel/vdso.c b/arch/mips/kernel/vdso.c index e5cdfd6..0f1af58 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) -- cgit v1.1 From accb61fe7bb0f5c2a4102239e4981650f9048519 Mon Sep 17 00:00:00 2001 From: Jason Baron Date: Fri, 23 Mar 2012 15:02:51 -0700 Subject: coredump: add VM_NODUMP, MADV_NODUMP, MADV_CLEAR_NODUMP Since we no longer need the VM_ALWAYSDUMP flag, let's use the freed bit for 'VM_NODUMP' flag. The idea is is to add a new madvise() flag: MADV_DONTDUMP, which can be set by applications to specifically request memory regions which should not dump core. The specific application I have in mind is qemu: we can add a flag there that wouldn't dump all of guest memory when qemu dumps core. This flag might also be useful for security sensitive apps that want to absolutely make sure that parts of memory are not dumped. To clear the flag use: MADV_DODUMP. [akpm@linux-foundation.org: s/MADV_NODUMP/MADV_DONTDUMP/, s/MADV_CLEAR_NODUMP/MADV_DODUMP/, per Roland] [akpm@linux-foundation.org: fix up the architectures which broke] Signed-off-by: Jason Baron Acked-by: Roland McGrath Cc: Chris Metcalf Cc: Avi Kivity Cc: Ralf Baechle Cc: Richard Henderson Cc: Ivan Kokshaysky Cc: Matt Turner Cc: "James E.J. Bottomley" Cc: Helge Deller Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- arch/mips/include/asm/mman.h | 4 ++++ 1 file changed, 4 insertions(+) (limited to 'arch/mips') diff --git a/arch/mips/include/asm/mman.h b/arch/mips/include/asm/mman.h index 785b4ea..46d3da0 100644 --- a/arch/mips/include/asm/mman.h +++ b/arch/mips/include/asm/mman.h @@ -80,6 +80,10 @@ #define MADV_HUGEPAGE 14 /* Worth backing with hugepages */ #define MADV_NOHUGEPAGE 15 /* Not worth backing with hugepages */ +#define MADV_DONTDUMP 16 /* Explicity exclude from the core dump, + overrides the coredump filter bits */ +#define MADV_DODUMP 17 /* Clear the MADV_NODUMP flag */ + /* compatibility flags */ #define MAP_FILE 0 -- cgit v1.1