[ARM] 3809/3: get rid of 4 megabyte kernel image size limit (2552fc27) · Commits · 戴 / test

We currently have a hardcoded 4 megabyte uncompressed kernel image size limit, which is easily exceeded by, for example, enabling some of the various kernel debugging options. When setting up the initial page tables (which is where this 4M limit is hardcoded), it's actually relatively easy to find out the true size of the uncompressed kernel image and create enough page table entries for things to fit, so this patch makes it so. In the decompressor, we also need to know the size of the uncompressed kernel image, to figure out whether there is any chance that uncompressing the kernel might overwrite the compressed kernel image stored elsewhere in memory. We don't have that info at this boot stage, though, so we approximate the size of the uncompressed kernel by taking the compressed kernel image size and allowing for a maximum 4x expansion. Signed-off-by:

Lennert Buytenhek <buytenh@wantstofly.org> Signed-off-by:

Russell King <rmk+kernel@arm.linux.org.uk>

arch/arm/boot/compressed/head.S

+2 −1

Original line number	Diff line number	Diff line
		@@ -237,7 +237,8 @@ not_relocated: mov r0, #0
		*/
		cmp r4, r2
		bhs wont_overwrite
		add r0, r4, #4096*1024 @ 4MB largest kernel size
		sub r3, sp, r5 @ > compressed kernel size
		add r0, r4, r3, lsl #2 @ allow for 4x expansion
		cmp r0, r5
		bls wont_overwrite

arch/arm/kernel/head.S

+9 −9

Original line number	Diff line number	Diff line
		@@ -234,18 +234,18 @@ __create_page_tables:

		/*
		* Now setup the pagetables for our kernel direct
		* mapped region. We round TEXTADDR down to the
		* nearest megabyte boundary. It is assumed that
		* the kernel fits within 4 contigous 1MB sections.
		* mapped region.
		*/
		add r0, r4, #(TEXTADDR & 0xff000000) >> 18 @ start of kernel
		str r3, [r0, #(TEXTADDR & 0x00f00000) >> 18]!
		add r3, r3, #1 << 20
		str r3, [r0, #4]! @ KERNEL + 1MB
		add r3, r3, #1 << 20
		str r3, [r0, #4]! @ KERNEL + 2MB
		add r3, r3, #1 << 20
		str r3, [r0, #4] @ KERNEL + 3MB

		ldr r6, =(_end - PAGE_OFFSET - 1) @ r6 = number of sections
		mov r6, r6, lsr #20 @ needed for kernel minus 1

		1: add r3, r3, #1 << 20
		str r3, [r0, #4]!
		subs r6, r6, #1
		bgt 1b

		/*
		* Then map first 1MB of ram in case it contains our boot params.

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