[v2,3/6] kexec_file: Allow skipping checksum calculation for some segments.

Commit Message

Thiago Jung Bauermann Aug. 22, 2016, 10:12 p.m. UTC

Am Montag, 22 August 2016, 11:36:43 schrieb Dave Young:
> On 08/22/16 at 12:25am, Thiago Jung Bauermann wrote:
> > Am Montag, 22 August 2016, 11:17:45 schrieb Dave Young:
> > > On 08/18/16 at 06:09pm, Thiago Jung Bauermann wrote:
> > > > Am Donnerstag, 18 August 2016, 17:03:30 schrieb Dave Young:
> > > > > On 08/13/16 at 12:18am, Thiago Jung Bauermann wrote:
> > > > > > Adds checksum argument to kexec_add_buffer specifying whether
> > > > > > the
> > > > > > given
> > > > > > segment should be part of the checksum calculation.
> > > > > 
> > > > > Since it is used with add buffer, could it be added to kbuf as a
> > > > > new
> > > > > field?
> > > > 
> > > > I was on the fence about adding it as a new argument to
> > > > kexec_add_buffer
> > > > or as a new field to struct kexec_buf. Both alternatives make sense
> > > > to
> > > > me. I implemented your suggestion in the patch below, what do you
> > > > think?>
> > > > 
> > > > > Like kbuf.no_checksum, default value is 0 that means checksum is
> > > > > needed
> > > > > if it is 1 then no need a checksum.
> > > > 
> > > > It's an interesting idea and I implemented it that way, though in
> > > > practice all current users of struct kexec_buf put it on the stack
> > > > so
> > > > the field needs to be initialized explicitly.
> > > 
> > > No need to set it as false because it will be initialized to 0 by
> > > default?
> > 
> > As far as I know, variables on the stack are not initialized. Only
> > global
> > and static variables are.
> 
> But designated initializers will do it.

Here is the new version, relying on the default value for
kexec_buf.skip_checksum. A nice side effect is that I don't have to
cc the x86 maintainers anymore.

What do you think?

Patch

diff --git a/include/linux/kexec.h b/include/linux/kexec.h
index 4559a1a01b0a..e5b3d99cbe50 100644
--- a/include/linux/kexec.h
+++ b/include/linux/kexec.h
@@ -100,6 +100,9 @@  struct kexec_segment {
 	size_t bufsz;
 	unsigned long mem;
 	size_t memsz;
+
+	/* Whether this segment is ignored in the checksum calculation. */
+	bool skip_checksum;
 };
 
 #ifdef CONFIG_COMPAT
@@ -151,15 +154,16 @@  struct kexec_file_ops {
 
 /**
  * struct kexec_buf - parameters for finding a place for a buffer in memory
- * @image:	kexec image in which memory to search.
- * @buffer:	Contents which will be copied to the allocated memory.
- * @bufsz:	Size of @buffer.
- * @mem:	On return will have address of the buffer in memory.
- * @memsz:	Size for the buffer in memory.
- * @buf_align:	Minimum alignment needed.
- * @buf_min:	The buffer can't be placed below this address.
- * @buf_max:	The buffer can't be placed above this address.
- * @top_down:	Allocate from top of memory.
+ * @image:		kexec image in which memory to search.
+ * @buffer:		Contents which will be copied to the allocated memory.
+ * @bufsz:		Size of @buffer.
+ * @mem:		On return will have address of the buffer in memory.
+ * @memsz:		Size for the buffer in memory.
+ * @buf_align:		Minimum alignment needed.
+ * @buf_min:		The buffer can't be placed below this address.
+ * @buf_max:		The buffer can't be placed above this address.
+ * @top_down:		Allocate from top of memory.
+ * @skip_checksum:	Don't verify checksum for this buffer in purgatory.
  */
 struct kexec_buf {
 	struct kimage *image;
@@ -171,6 +175,7 @@  struct kexec_buf {
 	unsigned long buf_min;
 	unsigned long buf_max;
 	bool top_down;
+	bool skip_checksum;
 };
 
 int __weak arch_kexec_walk_mem(struct kexec_buf *kbuf,
diff --git a/kernel/kexec_file.c b/kernel/kexec_file.c
index c8418d62e2fc..f6e9958bf578 100644
--- a/kernel/kexec_file.c
+++ b/kernel/kexec_file.c
@@ -658,6 +658,7 @@  int kexec_add_buffer(struct kexec_buf *kbuf)
 	ksegment->bufsz = kbuf->bufsz;
 	ksegment->mem = kbuf->mem;
 	ksegment->memsz = kbuf->memsz;
+	ksegment->skip_checksum = kbuf->skip_checksum;
 	kbuf->image->nr_segments++;
 	return 0;
 }
@@ -672,7 +673,6 @@  static int kexec_calculate_store_digests(struct kimage *image)
 	char *digest;
 	void *zero_buf;
 	struct kexec_sha_region *sha_regions;
-	struct purgatory_info *pi = &image->purgatory_info;
 
 	zero_buf = __va(page_to_pfn(ZERO_PAGE(0)) << PAGE_SHIFT);
 	zero_buf_sz = PAGE_SIZE;
@@ -712,11 +712,7 @@  static int kexec_calculate_store_digests(struct kimage *image)
 		struct kexec_segment *ksegment;
 
 		ksegment = &image->segment[i];
-		/*
-		 * Skip purgatory as it will be modified once we put digest
-		 * info in purgatory.
-		 */
-		if (ksegment->kbuf == pi->purgatory_buf)
+		if (ksegment->skip_checksum)
 			continue;
 
 		ret = crypto_shash_update(desc, ksegment->kbuf,
@@ -788,7 +784,7 @@  static int __kexec_load_purgatory(struct kimage *image, unsigned long min,
 	Elf_Shdr *sechdrs = NULL;
 	struct kexec_buf kbuf = { .image = image, .bufsz = 0, .buf_align = 1,
 				  .buf_min = min, .buf_max = max,
-				  .top_down = top_down };
+				  .top_down = top_down, .skip_checksum = true };
 
 	/*
 	 * sechdrs_c points to section headers in purgatory and are read
@@ -893,7 +889,10 @@  static int __kexec_load_purgatory(struct kimage *image, unsigned long min,
 	if (kbuf.buf_align < bss_align)
 		kbuf.buf_align = bss_align;
 
-	/* Add buffer to segment list */
+	/*
+	 * Add buffer to segment list. Don't checksum the segment as
+	 * it will be modified once we put digest info in purgatory.
+	 */
 	ret = kexec_add_buffer(&kbuf);
 	if (ret)
 		goto out;