From: Fabiano Rosas <farosas@linux.ibm.com>
To: kvm-ppc@vger.kernel.org
Cc: linuxppc-dev@lists.ozlabs.org, christophe.leroy@c-s.fr,
npiggin@gmail.com
Subject: [PATCH v2 1/3] KVM: PPC: Book3S HV: Fix copy_tofrom_guest routines
Date: Thu, 05 Aug 2021 21:26:14 +0000 [thread overview]
Message-ID: <20210805212616.2641017-2-farosas@linux.ibm.com> (raw)
In-Reply-To: <20210805212616.2641017-1-farosas@linux.ibm.com>
The __kvmhv_copy_tofrom_guest_radix function was introduced along with
nested HV guest support. It uses the platform's Radix MMU quadrants to
provide a nested hypervisor with fast access to its nested guests
memory (H_COPY_TOFROM_GUEST hypercall). It has also since been added
as a fast path for the kvmppc_ld/st routines which are used during
instruction emulation.
The commit def0bfdbd603 ("powerpc: use probe_user_read() and
probe_user_write()") changed the low level copy function from
raw_copy_from_user to probe_user_read, which adds a check to
access_ok. In powerpc that is:
static inline bool __access_ok(unsigned long addr, unsigned long size)
{
return addr < TASK_SIZE_MAX && size <= TASK_SIZE_MAX - addr;
}
and TASK_SIZE_MAX is 0x0010000000000000UL for 64-bit, which means that
setting the two MSBs of the effective address (which correspond to the
quadrant) now cause access_ok to reject the access.
This was not caught earlier because the most common code path via
kvmppc_ld/st contains a fallback (kvm_read_guest) that is likely to
succeed for L1 guests. For nested guests there is no fallback.
Another issue is that probe_user_read (now __copy_from_user_nofault)
does not return the number of bytes not copied in case of failure, so
the destination memory is not being cleared anymore in
kvmhv_copy_from_guest_radix:
ret = kvmhv_copy_tofrom_guest_radix(vcpu, eaddr, to, NULL, n);
if (ret > 0) <-- always false!
memset(to + (n - ret), 0, ret);
This patch fixes both issues by skipping access_ok and open-coding the
low level __copy_to/from_user_inatomic.
Fixes: def0bfdbd603 ("powerpc: use probe_user_read() and probe_user_write()")
Signed-off-by: Fabiano Rosas <farosas@linux.ibm.com>
---
arch/powerpc/kvm/book3s_64_mmu_radix.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)
diff --git a/arch/powerpc/kvm/book3s_64_mmu_radix.c b/arch/powerpc/kvm/book3s_64_mmu_radix.c
index b5905ae4377c..44eb7b1ef289 100644
--- a/arch/powerpc/kvm/book3s_64_mmu_radix.c
+++ b/arch/powerpc/kvm/book3s_64_mmu_radix.c
@@ -65,10 +65,12 @@ unsigned long __kvmhv_copy_tofrom_guest_radix(int lpid, int pid,
}
isync();
+ pagefault_disable();
if (is_load)
- ret = copy_from_user_nofault(to, (const void __user *)from, n);
+ ret = __copy_from_user_inatomic(to, (const void __user *)from, n);
else
- ret = copy_to_user_nofault((void __user *)to, from, n);
+ ret = __copy_to_user_inatomic((void __user *)to, from, n);
+ pagefault_enable();
/* switch the pid first to avoid running host with unallocated pid */
if (quadrant = 1 && pid != old_pid)
--
2.29.2
next prev parent reply other threads:[~2021-08-05 21:26 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-08-05 21:26 [PATCH v2 0/3] KVM: PPC: Book3S HV: kvmhv_copy_tofrom_guest_radix changes Fabiano Rosas
2021-08-05 21:26 ` Fabiano Rosas [this message]
2021-08-06 10:09 ` [PATCH v2 1/3] KVM: PPC: Book3S HV: Fix copy_tofrom_guest routines Nicholas Piggin
2021-08-05 21:26 ` [PATCH v2 2/3] KVM: PPC: Book3S HV: Add sanity check to copy_tofrom_guest Fabiano Rosas
2021-08-06 10:10 ` Nicholas Piggin
2021-08-05 21:26 ` [PATCH v2 3/3] KVM: PPC: Book3S HV: Stop exporting symbols from book3s_64_mmu_radix Fabiano Rosas
2021-08-27 13:15 ` [PATCH v2 0/3] KVM: PPC: Book3S HV: kvmhv_copy_tofrom_guest_radix changes Michael Ellerman
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