From 93de2a6a4b91b72607136dd656edf03fb399d27f Mon Sep 17 00:00:00 2001 From: Sean Christopherson Date: Wed, 23 Sep 2026 09:37:21 -0700 Subject: KVM: SEV: Do cache maintenance on the source VM during intra-host migration Manually perform cache maintenance on the source VM during intra-host migration to ensure no stale data is left in CPU caches after the VM is destroyed. Because the source VM is "converted" to a non-SEV VM, KVM's memory reclaim flows won't trigger cache maintenance, e.g. when all guest memory is reclaimed in response to detaching from the mmu_notifier. Note, relying on the destination VM to do cache maintenance isn't an option as KVM doesn't require identical guest memory configurations, i.e. the source VM may have access to memory that the destination VM does not. Enforcing equivalent memory configurations is infeasible, as it would require a *deep* comparison of memslots, e.g. to verify that not only are the memslot identical, but what the memslots point at is also identical. Fixes: b56639318bb2 ("KVM: SEV: Add support for SEV intra host migration") Cc: stable@vger.kernel.org Reported-by: Stefan Teodorescu Signed-off-by: Sean Christopherson Message-ID: <20260923163721.1584779-3-seanjc@google.com> Signed-off-by: Paolo Bonzini --- lib/usercopy.c | 81 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 81 insertions(+) create mode 100644 lib/usercopy.c (limited to 'lib/usercopy.c') diff --git a/lib/usercopy.c b/lib/usercopy.c new file mode 100644 index 000000000..e2f0bf104 --- /dev/null +++ b/lib/usercopy.c @@ -0,0 +1,81 @@ +// SPDX-License-Identifier: GPL-2.0 +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include + +/* out-of-line parts */ + +#if !defined(INLINE_COPY_USER) +unsigned long _copy_from_user(void *to, const void __user *from, unsigned long n) +{ + return _inline_copy_from_user(to, from, n); +} +EXPORT_SYMBOL(_copy_from_user); + +unsigned long _copy_to_user(void __user *to, const void *from, unsigned long n) +{ + return _inline_copy_to_user(to, from, n); +} +EXPORT_SYMBOL(_copy_to_user); +#endif + +/** + * check_zeroed_user: check if a userspace buffer only contains zero bytes + * @from: Source address, in userspace. + * @size: Size of buffer. + * + * This is effectively shorthand for "memchr_inv(from, 0, size) == NULL" for + * userspace addresses (and is more efficient because we don't care where the + * first non-zero byte is). + * + * Returns: + * * 0: There were non-zero bytes present in the buffer. + * * 1: The buffer was full of zero bytes. + * * -EFAULT: access to userspace failed. + */ +int check_zeroed_user(const void __user *from, size_t size) +{ + unsigned long val; + uintptr_t align = (uintptr_t) from % sizeof(unsigned long); + + if (unlikely(size == 0)) + return 1; + + from -= align; + size += align; + + if (!user_read_access_begin(from, size)) + return -EFAULT; + + unsafe_get_user(val, (unsigned long __user *) from, err_fault); + if (align) + val &= ~aligned_byte_mask(align); + + while (size > sizeof(unsigned long)) { + if (unlikely(val)) + goto done; + + from += sizeof(unsigned long); + size -= sizeof(unsigned long); + + unsafe_get_user(val, (unsigned long __user *) from, err_fault); + } + + if (size < sizeof(unsigned long)) + val &= aligned_byte_mask(size); + +done: + user_read_access_end(); + return (val == 0); +err_fault: + user_read_access_end(); + return -EFAULT; +} +EXPORT_SYMBOL(check_zeroed_user); -- cgit v1.3.1