[PATCH v2 1/1] arm: do not copy magic 4 bytes of appended DTB in zImage

[PATCH v2 1/1] arm: do not copy magic 4 bytes of appended DTB in zImage

[Alexander Egorenkov]

If the passed zImage happens to have a DTB appended, then the magic 4 bytes
of the DTB are copied together with the kernel image. This leads to
failed kexec boots because the decompressor finds the aforementioned
DTB magic and falsely tries to replace the DTB passed in the register r2
with the non-existent appended one.

Signed-off-by: Alexander Egorenkov <egorenar-dev@posteo.net>
---

v1 -> v2:
  * Add a comment explaining the reason for introducing kernel_buf_size 

 kexec/arch/arm/kexec-zImage-arm.c | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/kexec/arch/arm/kexec-zImage-arm.c b/kexec/arch/arm/kexec-zImage-arm.c
index 925a9be..f4c23bf 100644
--- a/kexec/arch/arm/kexec-zImage-arm.c
+++ b/kexec/arch/arm/kexec-zImage-arm.c
@@ -382,6 +382,7 @@ int zImage_arm_load(int argc, char **argv, const char *buf, off_t len,
 	unsigned int atag_offset = 0x1000; /* 4k offset from memory start */
 	unsigned int extra_size = 0x8000; /* TEXT_OFFSET */
 	const struct zimage_tag *tag;
+	size_t kernel_buf_size;
 	size_t kernel_mem_size;
 	const char *command_line;
 	char *modified_cmdline = NULL;
@@ -537,6 +538,15 @@ int zImage_arm_load(int argc, char **argv, const char *buf, off_t len,
 		}
 	}
 
+	/*
+	 * Save the length of the compressed kernel image w/o the appended DTB.
+	 * This will be required later on when the kernel image contained
+	 * in the zImage will be loaded into a kernel memory segment.
+	 * And we want to load ONLY the compressed kernel image from the zImage
+	 * and discard the appended DTB.
+	 */
+	kernel_buf_size = len;
+
 	/*
 	 * Always extend the zImage by four bytes to ensure that an appended
 	 * DTB image always sees an initialised value after _edata.
@@ -759,7 +769,7 @@ int zImage_arm_load(int argc, char **argv, const char *buf, off_t len,
 		add_segment(info, dtb_buf, dtb_length, dtb_offset, dtb_length);
 	}
 
-	add_segment(info, buf, len, kernel_base, kernel_mem_size);
+	add_segment(info, buf, kernel_buf_size, kernel_base, kernel_mem_size);
 
 	info->entry = (void*)kernel_base;
 
-- 
2.31.1


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Re: [PATCH v2 1/1] arm: do not copy magic 4 bytes of appended DTB in zImage

[Simon Horman]

On Mon, Apr 12, 2021 at 01:18:05PM +0200, Alexander Egorenkov wrote:
> If the passed zImage happens to have a DTB appended, then the magic 4 bytes
> of the DTB are copied together with the kernel image. This leads to
> failed kexec boots because the decompressor finds the aforementioned
> DTB magic and falsely tries to replace the DTB passed in the register r2
> with the non-existent appended one.
> 
> Signed-off-by: Alexander Egorenkov <egorenar-dev@posteo.net>
> ---
> 
> v1 -> v2:
>   * Add a comment explaining the reason for introducing kernel_buf_size 

Thanks Alexander, applied.

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