5.15-stable review patch. If anyone has any objections, please let me know.
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From: Adam Dunlap acdunlap@google.com
[ Upstream commit f79936545fb122856bd78b189d3c7ee59928c751 ]
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 Signed-off-by: Sasha Levin sashal@kernel.org --- 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)