Accept elf files that are valid but have sections that can not be mmap'ed for some...

Plan9 kernel binaries don't neatly align their ELF sections to our
page boundaries.

Signed-off-by: Ronald G. Minnich <rminnich@gmail.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

diff --git a/Documentation/lguest/lguest.c b/Documentation/lguest/lguest.c
index fa838e2..401d26b 100644 (file)
--- a/Documentation/lguest/lguest.c
+++ b/Documentation/lguest/lguest.c
@@ -15,6 +15,7 @@
 #include <stdlib.h>
 #include <elf.h>
 #include <sys/mman.h>
+#include <sys/param.h>
 #include <sys/types.h>
 #include <sys/stat.h>
 #include <sys/wait.h>
@@ -162,6 +163,30 @@ static unsigned long entry_point(void *start, void *end,
        errx(1, "Is this image a genuine lguest?");
 }
 
+/* This routine is used to load the kernel or initrd.  It tries mmap, but if
+ * that fails (Plan 9's kernel file isn't nicely aligned on page boundaries),
+ * it falls back to reading the memory in. */
+static void map_at(int fd, void *addr, unsigned long offset, unsigned long len)
+{
+       ssize_t r;
+
+       /* We map writable even though for some segments are marked read-only.
+        * The kernel really wants to be writable: it patches its own
+        * instructions.
+        *
+        * MAP_PRIVATE means that the page won't be copied until a write is
+        * done to it.  This allows us to share untouched memory between
+        * Guests. */
+       if (mmap(addr, len, PROT_READ|PROT_WRITE|PROT_EXEC,
+                MAP_FIXED|MAP_PRIVATE, fd, offset) != MAP_FAILED)
+               return;
+
+       /* pread does a seek and a read in one shot: saves a few lines. */
+       r = pread(fd, addr, len, offset);
+       if (r != len)
+               err(1, "Reading offset %lu len %lu gave %zi", offset, len, r);
+}
+
 /* This routine takes an open vmlinux image, which is in ELF, and maps it into
  * the Guest memory.  ELF = Embedded Linking Format, which is the format used
  * by all modern binaries on Linux including the kernel.
@@ -176,7 +201,6 @@ static unsigned long entry_point(void *start, void *end,
 static unsigned long map_elf(int elf_fd, const Elf32_Ehdr *ehdr,
                             unsigned long *page_offset)
 {
-       void *addr;
        Elf32_Phdr phdr[ehdr->e_phnum];
        unsigned int i;
        unsigned long start = -1UL, end = 0;
@@ -227,23 +251,9 @@ static unsigned long map_elf(int elf_fd, const Elf32_Ehdr *ehdr,
                if (phdr[i].p_paddr + phdr[i].p_filesz > end)
                        end = phdr[i].p_paddr + phdr[i].p_filesz;
 
-               /* We map this section of the file at its physical address.  We
-                * map it read & write even if the header says this segment is
-                * read-only.  The kernel really wants to be writable: it
-                * patches its own instructions which would normally be
-                * read-only.
-                *
-                * MAP_PRIVATE means that the page won't be copied until a
-                * write is done to it.  This allows us to share much of the
-                * kernel memory between Guests. */
-               addr = mmap((void *)phdr[i].p_paddr,
-                           phdr[i].p_filesz,
-                           PROT_READ|PROT_WRITE|PROT_EXEC,
-                           MAP_FIXED|MAP_PRIVATE,
-                           elf_fd, phdr[i].p_offset);
-               if (addr != (void *)phdr[i].p_paddr)
-                       err(1, "Mmaping vmlinux seg %i gave %p not %p",
-                           i, addr, (void *)phdr[i].p_paddr);
+               /* We map this section of the file at its physical address. */
+               map_at(elf_fd, (void *)phdr[i].p_paddr,
+                      phdr[i].p_offset, phdr[i].p_filesz);
        }
 
        return entry_point((void *)start, (void *)end, *page_offset);
@@ -402,27 +412,20 @@ static unsigned long load_initrd(const char *name, unsigned long mem)
        int ifd;
        struct stat st;
        unsigned long len;
-       void *iaddr;
 
        ifd = open_or_die(name, O_RDONLY);
        /* fstat() is needed to get the file size. */
        if (fstat(ifd, &st) < 0)
                err(1, "fstat() on initrd '%s'", name);
 
-       /* The length needs to be rounded up to a page size: mmap needs the
-        * address to be page aligned. */
+       /* We map the initrd at the top of memory, but mmap wants it to be
+        * page-aligned, so we round the size up for that. */
        len = page_align(st.st_size);
-       /* We map the initrd at the top of memory. */
-       iaddr = mmap((void *)mem - len, st.st_size,
-                    PROT_READ|PROT_EXEC|PROT_WRITE,
-                    MAP_FIXED|MAP_PRIVATE, ifd, 0);
-       if (iaddr != (void *)mem - len)
-               err(1, "Mmaping initrd '%s' returned %p not %p",
-                   name, iaddr, (void *)mem - len);
+       map_at(ifd, (void *)mem - len, 0, st.st_size);
        /* Once a file is mapped, you can close the file descriptor.  It's a
         * little odd, but quite useful. */
        close(ifd);
-       verbose("mapped initrd %s size=%lu @ %p\n", name, st.st_size, iaddr);
+       verbose("mapped initrd %s size=%lu @ %p\n", name, len, (void*)mem-len);
 
        /* We return the initrd size. */
        return len;