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Fabiano Rosas 5d7d6dac8f KVM: PPC: Book3S HV: Fix copy_tofrom_guest routines 
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 def0bfdbd6 ("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: def0bfdbd6 ("powerpc: use probe_user_read() and probe_user_write()")
Signed-off-by: Fabiano Rosas <farosas@linux.ibm.com>
Reviewed-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20210805212616.2641017-2-farosas@linux.ibm.com
2021-08-24 23:14:06 +10:00
..
boot powerpc updates for 5.14 2021-07-02 12:54:34 -07:00
configs TTY / Serial patches for 5.14-rc1 2021-07-05 14:08:24 -07:00
crypto crypto: powepc/sha1 - remove unneeded semicolon 2021-03-07 15:13:14 +11:00
include powerpc/book3s64/mm: update flush_tlb_range to flush page walk cache 2021-07-08 11:48:23 -07:00
kernel powerpc fixes for 5.14 #2 2021-07-09 10:26:52 -07:00
kexec powerpc updates for 5.14 2021-07-02 12:54:34 -07:00
kvm KVM: PPC: Book3S HV: Fix copy_tofrom_guest routines 2021-08-24 23:14:06 +10:00
lib powerpc: Only build restart_table.c for 64s 2021-07-01 22:50:54 +10:00
math-emu powerpc/64s: avoid reloading (H)SRR registers if they are still valid 2021-06-25 00:06:55 +10:00
mm powerpc fixes for 5.14 #2 2021-07-09 10:26:52 -07:00
net powerpc/bpf: Reject atomic ops in ppc32 JIT 2021-07-05 22:23:25 +10:00
perf powerpc updates for 5.14 2021-07-02 12:54:34 -07:00
platforms powerpc/smp: Fix fall-through warning for Clang 2021-07-14 11:10:40 -05:00
purgatory powerpc/kexec: Don't use .machine ppc64 in trampoline_64.S 2021-04-08 21:17:43 +10:00
sysdev powerpc/xive: Fix error handling when allocating an IPI 2021-07-05 22:23:25 +10:00
tools
xmon powerpc updates for 5.14 2021-07-02 12:54:34 -07:00
Kbuild
Kconfig powerpc updates for 5.14 2021-07-02 12:54:34 -07:00
Kconfig.debug powerpc: Make PPC_IRQ_SOFT_MASK_DEBUG depend on PPC64 2021-06-25 00:07:09 +10:00
Makefile Kbuild updates for v5.14 2021-07-10 11:01:38 -07:00
Makefile.postlink