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exec: set map length to zero when returning NULL

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When mapping physical memory into host's virtual address space,
'address_space_map' may return NULL if BounceBuffer is in_use.
Set and return '*plen = 0' to avoid later NULL pointer dereference.

Reported-by: Alexander Bulekov <alxndr@bu.edu>
Fixes: https://bugs.launchpad.net/qemu/+bug/1878259
Suggested-by: Paolo Bonzini <pbonzini@redhat.com>
Suggested-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Prasad J Pandit <pjp@fedoraproject.org>
Message-Id: <20200526111743.428367-1-ppandit@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Prasad J Pandit 2020-05-26 16:47:43 +05:30 committed by Paolo Bonzini
parent f2dfe54c74
commit 77f55eac6c
2 changed files with 3 additions and 1 deletions
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1
exec.c
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@ -3540,6 +3540,7 @@ void *address_space_map(AddressSpace *as,
if (!memory_access_is_direct(mr, is_write)) {
if (atomic_xchg(&bounce.in_use, true)) {
*plen = 0;
return NULL;
}
/* Avoid unbounded allocations */

3
include/exec/memory.h
View File

@ -2314,7 +2314,8 @@ bool address_space_access_valid(AddressSpace *as, hwaddr addr, hwaddr len,
/* address_space_map: map a physical memory region into a host virtual address
*
* May map a subset of the requested range, given by and returned in @plen.
* May return %NULL if resources needed to perform the mapping are exhausted.
* May return %NULL and set *@plen to zero(0), if resources needed to perform
* the mapping are exhausted.
* Use only for reads OR writes - not for read-modify-write operations.
* Use cpu_register_map_client() to know when retrying the map operation is
* likely to succeed.