arm64: head: Ignore bogus KASLR displacement on non-relocatable kernels

Even non-KASLR kernels can be built as relocatable, to work around broken bootloaders that violate the rules regarding physical placement of the kernel image - in this case, the physical offset modulo 2 MiB is used as the KASLR offset, and all absolute symbol references are fixed up in the usual way. This workaround is enabled by default.

CONFIG_RELOCATABLE can also be disabled entirely, in which case the relocation code and the code that captures the offset are omitted from the build. However, since commit aacd149b6238 ("arm64: head: avoid relocating the kernel twice for KASLR"), this code got out of sync, and we still add the offset to the kernel virtual address before populating the page tables even though we never capture it. This means we add a bogus value instead, breaking the boot entirely.

Fixes aacd149b6238 ("arm64: head: avoid relocating the kernel twice for KASLR")

Signed-off-by Ard Biesheuvel <[email protected]>

---
 arch/arm64/kernel/head.S | 2 ++
 1 file changed, 2 insertions(+)

arch/arm64/kernel/head.S +2 -0

index cefe6a73ee54..814b6587ccb7 100644
@@ -371,7 +371,9 @@ SYM_FUNC_END(create_idmap)
 SYM_FUNC_START_LOCAL(create_kernel_mapping)
 	adrp	x0, init_pg_dir
 	mov_q	x5, KIMAGE_VADDR		// compile time __va(_text)
+#ifdef CONFIG_RELOCATABLE
 	add	x5, x5, x23			// add KASLR displacement
+#endif
 	adrp	x6, _end			// runtime __pa(_end)
 	adrp	x3, _text			// runtime __pa(_text)
 	sub	x6, x6, x3			// _end - _text

Signature · 1 line

2.35.1

Even non-KASLR kernels can be built as relocatable, to work around broken bootloaders that violate the rules regarding physical placement of the kernel image - in this case, the physical offset modulo 2 MiB is used as the KASLR offset, and all absolute symbol references are fixed up in the usual way. This workaround is enabled by default.

CONFIG_RELOCATABLE can also be disabled entirely, in which case the relocation code and the code that captures the offset are omitted from the build. However, since commit aacd149b6238 ("arm64: head: avoid relocating the kernel twice for KASLR"), this code got out of sync, and we still add the offset to the kernel virtual address before populating the page tables even though we never capture it. This means we add a bogus value instead, breaking the boot entirely.

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