From f79936545fb122856bd78b189d3c7ee59928c751 Mon Sep 17 00:00:00 2001
From: Adam Dunlap <acdunlap@google.com>
Date: Mon, 11 Sep 2023 17:27:02 -0700
Subject: [PATCH] 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: 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
---
arch/x86/mm/maccess.c | 19 ++++++++++++++-----
1 file changed, 14 insertions(+), 5 deletions(-)
diff --git a/arch/x86/mm/maccess.c b/arch/x86/mm/maccess.c
index 5a53c2cc169cc..6993f026adec9 100644
--- a/arch/x86/mm/maccess.c
+++ b/arch/x86/mm/maccess.c
@@ -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)
--
2.30.2