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Date: Tue, 20 Oct 2020 01:25:59 -0700
From: John Hubbard <jhubbard@...dia.com>
To: "Kirill A. Shutemov" <kirill@...temov.name>,
Dave Hansen <dave.hansen@...ux.intel.com>,
Andy Lutomirski <luto@...nel.org>,
"Peter Zijlstra" <peterz@...radead.org>,
Paolo Bonzini <pbonzini@...hat.com>,
"Sean Christopherson" <sean.j.christopherson@...el.com>,
Vitaly Kuznetsov <vkuznets@...hat.com>,
Wanpeng Li <wanpengli@...cent.com>,
Jim Mattson <jmattson@...gle.com>,
Joerg Roedel <joro@...tes.org>
CC: David Rientjes <rientjes@...gle.com>,
Andrea Arcangeli <aarcange@...hat.com>,
Kees Cook <keescook@...omium.org>,
Will Drewry <wad@...omium.org>,
"Edgecombe, Rick P" <rick.p.edgecombe@...el.com>,
"Kleen, Andi" <andi.kleen@...el.com>,
Liran Alon <liran.alon@...cle.com>,
"Mike Rapoport" <rppt@...nel.org>, <x86@...nel.org>,
<kvm@...r.kernel.org>, <linux-mm@...ck.org>,
<linux-kernel@...r.kernel.org>,
"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Subject: Re: [RFCv2 08/16] KVM: Use GUP instead of copy_from/to_user() to
access guest memory
On 10/19/20 11:18 PM, Kirill A. Shutemov wrote:
> New helpers copy_from_guest()/copy_to_guest() to be used if KVM memory
> protection feature is enabled.
>
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
> ---
> include/linux/kvm_host.h | 4 ++
> virt/kvm/kvm_main.c | 90 +++++++++++++++++++++++++++++++---------
> 2 files changed, 75 insertions(+), 19 deletions(-)
>
> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index 05e3c2fb3ef7..380a64613880 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -504,6 +504,7 @@ struct kvm {
> struct srcu_struct irq_srcu;
> pid_t userspace_pid;
> unsigned int max_halt_poll_ns;
> + bool mem_protected;
> };
>
> #define kvm_err(fmt, ...) \
> @@ -728,6 +729,9 @@ void kvm_set_pfn_dirty(kvm_pfn_t pfn);
> void kvm_set_pfn_accessed(kvm_pfn_t pfn);
> void kvm_get_pfn(kvm_pfn_t pfn);
>
> +int copy_from_guest(void *data, unsigned long hva, int len, bool protected);
> +int copy_to_guest(unsigned long hva, const void *data, int len, bool protected);
> +
> void kvm_release_pfn(kvm_pfn_t pfn, bool dirty, struct gfn_to_pfn_cache *cache);
> int kvm_read_guest_page(struct kvm *kvm, gfn_t gfn, void *data, int offset,
> int len);
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index cf88233b819a..a9884cb8c867 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -2313,19 +2313,70 @@ static int next_segment(unsigned long len, int offset)
> return len;
> }
>
> +int copy_from_guest(void *data, unsigned long hva, int len, bool protected)
> +{
> + int offset = offset_in_page(hva);
> + struct page *page;
> + int npages, seg;
> +
> + if (!protected)
> + return __copy_from_user(data, (void __user *)hva, len);
> +
> + might_fault();
> + kasan_check_write(data, len);
> + check_object_size(data, len, false);
> +
> + while ((seg = next_segment(len, offset)) != 0) {
> + npages = get_user_pages_unlocked(hva, 1, &page, 0);
> + if (npages != 1)
> + return -EFAULT;
> + memcpy(data, page_address(page) + offset, seg);
Hi Kirill!
OK, so the copy_from_guest() is a read-only case for gup, which I think is safe
from a gup/pup + filesystem point of view, but see below about copy_to_guest()...
> + put_page(page);
> + len -= seg;
> + hva += seg;
> + offset = 0;
> + }
> +
> + return 0;
> +}
> +
> +int copy_to_guest(unsigned long hva, const void *data, int len, bool protected)
> +{
> + int offset = offset_in_page(hva);
> + struct page *page;
> + int npages, seg;
> +
> + if (!protected)
> + return __copy_to_user((void __user *)hva, data, len);
> +
> + might_fault();
> + kasan_check_read(data, len);
> + check_object_size(data, len, true);
> +
> + while ((seg = next_segment(len, offset)) != 0) {
> + npages = get_user_pages_unlocked(hva, 1, &page, FOLL_WRITE);
Should copy_to_guest() use pin_user_pages_unlocked() instead of gup_unlocked?
We wrote a "Case 5" in Documentation/core-api/pin_user_pages.rst, just for this
situation, I think:
CASE 5: Pinning in order to write to the data within the page
-------------------------------------------------------------
Even though neither DMA nor Direct IO is involved, just a simple case of "pin,
write to a page's data, unpin" can cause a problem. Case 5 may be considered a
superset of Case 1, plus Case 2, plus anything that invokes that pattern. In
other words, if the code is neither Case 1 nor Case 2, it may still require
FOLL_PIN, for patterns like this:
Correct (uses FOLL_PIN calls):
pin_user_pages()
write to the data within the pages
unpin_user_pages()
thanks,
--
John Hubbard
NVIDIA
> + if (npages != 1)
> + return -EFAULT;
> + memcpy(page_address(page) + offset, data, seg);
> + put_page(page);
> + len -= seg;
> + hva += seg;
> + offset = 0;
> + }
> +
> + return 0;
> +}
> +
> static int __kvm_read_guest_page(struct kvm_memory_slot *slot, gfn_t gfn,
> - void *data, int offset, int len)
> + void *data, int offset, int len,
> + bool protected)
> {
> - int r;
> unsigned long addr;
>
> addr = gfn_to_hva_memslot_prot(slot, gfn, NULL);
> if (kvm_is_error_hva(addr))
> return -EFAULT;
> - r = __copy_from_user(data, (void __user *)addr + offset, len);
> - if (r)
> - return -EFAULT;
> - return 0;
> + return copy_from_guest(data, addr + offset, len, protected);
> }
>
> int kvm_read_guest_page(struct kvm *kvm, gfn_t gfn, void *data, int offset,
> @@ -2333,7 +2384,8 @@ int kvm_read_guest_page(struct kvm *kvm, gfn_t gfn, void *data, int offset,
> {
> struct kvm_memory_slot *slot = gfn_to_memslot(kvm, gfn);
>
> - return __kvm_read_guest_page(slot, gfn, data, offset, len);
> + return __kvm_read_guest_page(slot, gfn, data, offset, len,
> + kvm->mem_protected);
> }
> EXPORT_SYMBOL_GPL(kvm_read_guest_page);
>
> @@ -2342,7 +2394,8 @@ int kvm_vcpu_read_guest_page(struct kvm_vcpu *vcpu, gfn_t gfn, void *data,
> {
> struct kvm_memory_slot *slot = kvm_vcpu_gfn_to_memslot(vcpu, gfn);
>
> - return __kvm_read_guest_page(slot, gfn, data, offset, len);
> + return __kvm_read_guest_page(slot, gfn, data, offset, len,
> + vcpu->kvm->mem_protected);
> }
> EXPORT_SYMBOL_GPL(kvm_vcpu_read_guest_page);
>
> @@ -2415,7 +2468,8 @@ int kvm_vcpu_read_guest_atomic(struct kvm_vcpu *vcpu, gpa_t gpa,
> EXPORT_SYMBOL_GPL(kvm_vcpu_read_guest_atomic);
>
> static int __kvm_write_guest_page(struct kvm_memory_slot *memslot, gfn_t gfn,
> - const void *data, int offset, int len)
> + const void *data, int offset, int len,
> + bool protected)
> {
> int r;
> unsigned long addr;
> @@ -2423,7 +2477,8 @@ static int __kvm_write_guest_page(struct kvm_memory_slot *memslot, gfn_t gfn,
> addr = gfn_to_hva_memslot(memslot, gfn);
> if (kvm_is_error_hva(addr))
> return -EFAULT;
> - r = __copy_to_user((void __user *)addr + offset, data, len);
> +
> + r = copy_to_guest(addr + offset, data, len, protected);
> if (r)
> return -EFAULT;
> mark_page_dirty_in_slot(memslot, gfn);
> @@ -2435,7 +2490,8 @@ int kvm_write_guest_page(struct kvm *kvm, gfn_t gfn,
> {
> struct kvm_memory_slot *slot = gfn_to_memslot(kvm, gfn);
>
> - return __kvm_write_guest_page(slot, gfn, data, offset, len);
> + return __kvm_write_guest_page(slot, gfn, data, offset, len,
> + kvm->mem_protected);
> }
> EXPORT_SYMBOL_GPL(kvm_write_guest_page);
>
> @@ -2444,7 +2500,8 @@ int kvm_vcpu_write_guest_page(struct kvm_vcpu *vcpu, gfn_t gfn,
> {
> struct kvm_memory_slot *slot = kvm_vcpu_gfn_to_memslot(vcpu, gfn);
>
> - return __kvm_write_guest_page(slot, gfn, data, offset, len);
> + return __kvm_write_guest_page(slot, gfn, data, offset, len,
> + vcpu->kvm->mem_protected);
> }
> EXPORT_SYMBOL_GPL(kvm_vcpu_write_guest_page);
>
> @@ -2560,7 +2617,7 @@ int kvm_write_guest_offset_cached(struct kvm *kvm, struct gfn_to_hva_cache *ghc,
> if (unlikely(!ghc->memslot))
> return kvm_write_guest(kvm, gpa, data, len);
>
> - r = __copy_to_user((void __user *)ghc->hva + offset, data, len);
> + r = copy_to_guest(ghc->hva + offset, data, len, kvm->mem_protected);
> if (r)
> return -EFAULT;
> mark_page_dirty_in_slot(ghc->memslot, gpa >> PAGE_SHIFT);
> @@ -2581,7 +2638,6 @@ int kvm_read_guest_offset_cached(struct kvm *kvm, struct gfn_to_hva_cache *ghc,
> unsigned long len)
> {
> struct kvm_memslots *slots = kvm_memslots(kvm);
> - int r;
> gpa_t gpa = ghc->gpa + offset;
>
> BUG_ON(len + offset > ghc->len);
> @@ -2597,11 +2653,7 @@ int kvm_read_guest_offset_cached(struct kvm *kvm, struct gfn_to_hva_cache *ghc,
> if (unlikely(!ghc->memslot))
> return kvm_read_guest(kvm, gpa, data, len);
>
> - r = __copy_from_user(data, (void __user *)ghc->hva + offset, len);
> - if (r)
> - return -EFAULT;
> -
> - return 0;
> + return copy_from_guest(data, ghc->hva + offset, len, kvm->mem_protected);
> }
> EXPORT_SYMBOL_GPL(kvm_read_guest_offset_cached);
>
>
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