Commit f7993654 authored by Adam Dunlap's avatar Adam Dunlap Committed by Ingo Molnar
Browse files

x86/sev-es: Allow copy_from_kernel_nofault() in earlier boot 



Previously, if copy_from_kernel_nofault() was called before
boot_cpu_data.x86_virt_bits was set up, then it would trigger undefined
behavior due to a shift by 64.

This ended up causing boot failures in the latest version of ubuntu2204
in the gcp project when using SEV-SNP.

Specifically, this function is called during an early #VC handler which
is triggered by a CPUID to check if NX is implemented.

Fixes: 1aa9aa8e ("x86/sev-es: Setup GHCB-based boot #VC handler")
Suggested-by: default avatarDave Hansen <dave.hansen@linux.intel.com>
Signed-off-by: default avatarAdam Dunlap <acdunlap@google.com>
Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
Tested-by: default avatarJacob Xu <jacobhxu@google.com>
Link: https://lore.kernel.org/r/20230912002703.3924521-2-acdunlap@google.com
parent f4c5ca98

arch/x86/mm/maccess.c

+14 −5
Original line number Diff line number Diff line
@@ -9,12 +9,21 @@ bool copy_from_kernel_nofault_allowed(const void *unsafe_src, size_t size) 
	unsigned long vaddr = (unsigned long)unsafe_src;



	/*

	 * Range covering the highest possible canonical userspace address

	 * as well as non-canonical address range. For the canonical range

	 * we also need to include the userspace guard page.

	 * Do not allow userspace addresses.  This disallows

	 * normal userspace and the userspace guard page:

	 */

	return vaddr >= TASK_SIZE_MAX + PAGE_SIZE &&

	       __is_canonical_address(vaddr, boot_cpu_data.x86_virt_bits);

	if (vaddr < TASK_SIZE_MAX + PAGE_SIZE)

		return false;



	/*

	 * Allow everything during early boot before 'x86_virt_bits'

	 * is initialized.  Needed for instruction decoding in early

	 * exception handlers.

	 */

	if (!boot_cpu_data.x86_virt_bits)

		return true;



	return __is_canonical_address(vaddr, boot_cpu_data.x86_virt_bits);

}

#else

bool copy_from_kernel_nofault_allowed(const void *unsafe_src, size_t size)