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

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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: 1aa9aa8ee517 ("x86/sev-es: Setup GHCB-based boot #VC handler")
Suggested-by: Dave Hansen <dave.hansen@linux.intel.com>
Signed-off-by: Adam Dunlap <acdunlap@google.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Tested-by: Jacob Xu <jacobhxu@google.com>
Link: https://lore.kernel.org/r/20230912002703.3924521-2-acdunlap@google.com
This commit is contained in:
Adam Dunlap 2023-09-11 17:27:02 -07:00 committed by Ingo Molnar
parent f4c5ca9850
commit f79936545f
1 changed files with 14 additions and 5 deletions
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19
arch/x86/mm/maccess.c
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@ -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)