[PATCH v2 12/13] arm64: add support for relocatable kernel
From: james.morse@arm.com (James Morse)
Date: 2016-01-08 10:18:11
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Hi Ard! On 30/12/15 15:26, Ard Biesheuvel wrote:
This adds support for runtime relocation of the kernel Image, by building it as a PIE (ET_DYN) executable and applying the dynamic relocations in the early boot code. Signed-off-by: Ard Biesheuvel <redacted> ---
quoted hunk ↗ jump to hunk
diff --git a/arch/arm64/kernel/head.S b/arch/arm64/kernel/head.S index 01a33e42ed70..ab582ee58b58 100644 --- a/arch/arm64/kernel/head.S +++ b/arch/arm64/kernel/head.S@@ -243,6 +253,16 @@ ENDPROC(stext) preserve_boot_args: mov x21, x0 // x21=FDT +#ifdef CONFIG_ARM64_RELOCATABLE_KERNEL + /* + * Mask off the bits of the random value supplied in x1 so it can serve + * as a KASLR displacement value which will move the kernel image to a + * random offset in the lower half of the VMALLOC area. + */ + mov x23, #(1 << (VA_BITS - 2)) - 1 + and x23, x23, x1, lsl #SWAPPER_BLOCK_SHIFT +#endif
I've managed to make this fail to boot by providing a seed that caused the kernel to overlap a 1G boundary on a 4K system. (It looks like your v3 may have the same issue - but I haven't tested it.)
+ adr_l x0, boot_args // record the contents of stp x21, x1, [x0] // x0 .. x3 at kernel entry stp x2, x3, [x0, #16]
Thanks! James