Change the way ELF coredumps are handled. Instead of unconditionally
skipping read-only pages, which can result in valuable non-text-related data not getting dumped, the ELF loader and the dynamic loader now mark read-only text pages NOCORE and the coredump code only checks (primarily) for complete inaccessibility of the page or NOCORE being set. Certain applications which map large amounts of read-only data will produce much larger cores. A new sysctl has been added, debug.elf_legacy_coredump, which will revert to the old behavior. This commit represents collaborative work by all parties involved. The PR contains a program demonstrating the problem. PR: kern/45994 Submitted by: "Peter Edwards" <pmedwards@eircom.net>, Archie Cobbs <archie@dellroad.org> Reviewed by: jdp, dillon MFC after: 7 days
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parent
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Notes:
svn2git
2020-12-20 02:59:44 +00:00
svn path=/head/; revision=107948
@ -38,7 +38,8 @@
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#include "debug.h"
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#include "rtld.h"
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static int protflags(int); /* Elf flags -> mmap protection */
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static int convert_prot(int); /* Elf flags -> mmap protection */
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static int convert_flags(int); /* Elf flags -> mmap flags */
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/*
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* Map a shared object into memory. The "fd" argument is a file descriptor,
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@ -75,6 +76,7 @@ map_object(int fd, const char *path, const struct stat *sb)
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Elf_Addr data_vlimit;
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caddr_t data_addr;
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int data_prot;
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int data_flags;
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Elf_Addr clear_vaddr;
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caddr_t clear_addr;
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caddr_t clear_page;
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@ -189,8 +191,8 @@ map_object(int fd, const char *path, const struct stat *sb)
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mapsize = base_vlimit - base_vaddr;
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base_addr = u.hdr.e_type == ET_EXEC ? (caddr_t) base_vaddr : NULL;
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mapbase = mmap(base_addr, mapsize, protflags(segs[0]->p_flags),
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MAP_PRIVATE, fd, base_offset);
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mapbase = mmap(base_addr, mapsize, convert_prot(segs[0]->p_flags),
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convert_flags(segs[0]->p_flags), fd, base_offset);
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if (mapbase == (caddr_t) -1) {
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_rtld_error("%s: mmap of entire address space failed: %s",
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path, strerror(errno));
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@ -209,10 +211,11 @@ map_object(int fd, const char *path, const struct stat *sb)
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data_vaddr = trunc_page(segs[i]->p_vaddr);
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data_vlimit = round_page(segs[i]->p_vaddr + segs[i]->p_filesz);
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data_addr = mapbase + (data_vaddr - base_vaddr);
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data_prot = protflags(segs[i]->p_flags);
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data_prot = convert_prot(segs[i]->p_flags);
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data_flags = convert_flags(segs[i]->p_flags) | MAP_FIXED;
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/* Do not call mmap on the first segment - this is redundant */
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if (i && mmap(data_addr, data_vlimit - data_vaddr, data_prot,
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MAP_PRIVATE|MAP_FIXED, fd, data_offset) == (caddr_t) -1) {
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data_flags, fd, data_offset) == (caddr_t) -1) {
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_rtld_error("%s: mmap of data failed: %s", path, strerror(errno));
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return NULL;
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}
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@ -315,7 +318,7 @@ obj_new(void)
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* flags for MMAP.
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*/
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static int
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protflags(int elfflags)
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convert_prot(int elfflags)
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{
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int prot = 0;
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if (elfflags & PF_R)
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@ -326,3 +329,17 @@ protflags(int elfflags)
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prot |= PROT_EXEC;
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return prot;
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}
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static int
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convert_flags(int elfflags)
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{
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int flags = MAP_PRIVATE; /* All mappings are private */
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/*
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* Readonly mappings are marked "MAP_NOCORE", because they can be
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* reconstructed by a debugger.
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*/
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if (!(elfflags & PF_W))
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flags |= MAP_NOCORE;
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return flags;
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}
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@ -87,6 +87,9 @@ SYSCTL_INT(_debug, OID_AUTO, elf32_trace, CTLFLAG_RW, &elf_trace, 0, "");
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#else
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SYSCTL_INT(_debug, OID_AUTO, elf64_trace, CTLFLAG_RW, &elf_trace, 0, "");
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#endif
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static int elf_legacy_coredump = 0;
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SYSCTL_INT(_debug, OID_AUTO, elf_legacy_coredump, CTLFLAG_RW,
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&elf_legacy_coredump, 0, "");
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static Elf_Brandinfo *elf_brand_list[MAX_BRANDS];
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extern int fallback_elf_brand;
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@ -349,7 +352,7 @@ __elfN(load_section)(struct proc *p, struct vmspace *vmspace,
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{
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size_t map_len;
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vm_offset_t map_addr;
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int error, rv;
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int error, rv, cow;
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size_t copy_len;
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vm_offset_t file_addr;
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vm_offset_t data_buf = 0;
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@ -392,6 +395,11 @@ __elfN(load_section)(struct proc *p, struct vmspace *vmspace,
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if (map_len != 0) {
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vm_object_reference(object);
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/* cow flags: don't dump readonly sections in core */
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cow = MAP_COPY_ON_WRITE | MAP_PREFAULT |
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(prot & VM_PROT_WRITE ? 0 : MAP_DISABLE_COREDUMP);
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rv = __elfN(map_insert)(&vmspace->vm_map,
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object,
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file_addr, /* file offset */
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@ -399,7 +407,7 @@ __elfN(load_section)(struct proc *p, struct vmspace *vmspace,
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map_addr + map_len,/* virtual end */
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prot,
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VM_PROT_ALL,
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MAP_COPY_ON_WRITE | MAP_PREFAULT);
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cow);
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if (rv != KERN_SUCCESS) {
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vm_object_deallocate(object);
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return (EINVAL);
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@ -1042,17 +1050,29 @@ each_writable_segment(p, func, closure)
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entry = entry->next) {
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vm_object_t obj;
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if ((entry->eflags & MAP_ENTRY_IS_SUB_MAP) ||
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(entry->protection & (VM_PROT_READ|VM_PROT_WRITE)) !=
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(VM_PROT_READ|VM_PROT_WRITE))
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continue;
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/*
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* Don't dump inaccessible mappings, deal with legacy
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* coredump mode.
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*
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* Note that read-only segments related to the elf binary
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* are marked MAP_ENTRY_NOCOREDUMP now so we no longer
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* need to arbitrarily ignore such segments.
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*/
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if (elf_legacy_coredump) {
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if ((entry->protection & VM_PROT_RW) != VM_PROT_RW)
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continue;
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} else {
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if ((entry->protection & VM_PROT_ALL) == 0)
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continue;
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}
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/*
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** Dont include memory segment in the coredump if
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** MAP_NOCORE is set in mmap(2) or MADV_NOCORE in
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** madvise(2).
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*/
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if (entry->eflags & MAP_ENTRY_NOCOREDUMP)
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* Dont include memory segment in the coredump if
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* MAP_NOCORE is set in mmap(2) or MADV_NOCORE in
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* madvise(2). Do not dump submaps (i.e. parts of the
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* kernel map).
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*/
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if (entry->eflags & (MAP_ENTRY_NOCOREDUMP|MAP_ENTRY_IS_SUB_MAP))
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continue;
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if ((obj = entry->object.vm_object) == NULL)
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@ -81,6 +81,7 @@ typedef u_char vm_prot_t; /* protection codes */
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#define VM_PROT_OVERRIDE_WRITE ((vm_prot_t) 0x08) /* copy-on-write */
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#define VM_PROT_ALL (VM_PROT_READ|VM_PROT_WRITE|VM_PROT_EXECUTE)
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#define VM_PROT_RW (VM_PROT_READ|VM_PROT_WRITE)
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#define VM_PROT_DEFAULT VM_PROT_ALL
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union vm_map_object;
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