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[Qemu-devel] [PULL v2 01/24] linux-user: Avoid possible misalignment in

From: riku . voipio
Subject: [Qemu-devel] [PULL v2 01/24] linux-user: Avoid possible misalignment in host_to_target_siginfo()
Date: Tue, 28 Jun 2016 22:12:35 +0300

From: Peter Maydell <address@hidden>

host_to_target_siginfo() is implemented by a combination of
host_to_target_siginfo_noswap() followed by tswap_siginfo().
The first of these two functions assumes that the target_siginfo_t
it is writing to is correctly aligned, but the pointer passed
into host_to_target_siginfo() is directly from the guest and
might be misaligned. Use a local variable to avoid this problem.
(tswap_siginfo() does now correctly handle a misaligned destination.)

We have to add a memset() to host_to_target_siginfo_noswap()
to avoid some false positive "may be used uninitialized" warnings
from gcc about subfields of the _sifields union if it chooses to
inline both tswap_siginfo() and host_to_target_siginfo_noswap()
into host_to_target_siginfo().

Signed-off-by: Peter Maydell <address@hidden>
Reviewed-by: Laurent Vivier <address@hidden>
Signed-off-by: Peter Maydell <address@hidden>
 linux-user/signal.c | 13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/linux-user/signal.c b/linux-user/signal.c
index 1dadddf..e2d55ff 100644
--- a/linux-user/signal.c
+++ b/linux-user/signal.c
@@ -278,6 +278,14 @@ static inline void 
host_to_target_siginfo_noswap(target_siginfo_t *tinfo,
     tinfo->si_errno = 0;
     tinfo->si_code = info->si_code;
+    /* This memset serves two purposes:
+     * (1) ensure we don't leak random junk to the guest later
+     * (2) placate false positives from gcc about fields
+     *     being used uninitialized if it chooses to inline both this
+     *     function and tswap_siginfo() into host_to_target_siginfo().
+     */
+    memset(tinfo->_sifields._pad, 0, sizeof(tinfo->_sifields._pad));
     /* This is awkward, because we have to use a combination of
      * the si_code and si_signo to figure out which of the union's
      * members are valid. (Within the host kernel it is always possible
@@ -397,8 +405,9 @@ static void tswap_siginfo(target_siginfo_t *tinfo,
 void host_to_target_siginfo(target_siginfo_t *tinfo, const siginfo_t *info)
-    host_to_target_siginfo_noswap(tinfo, info);
-    tswap_siginfo(tinfo, tinfo);
+    target_siginfo_t tgt_tmp;
+    host_to_target_siginfo_noswap(&tgt_tmp, info);
+    tswap_siginfo(tinfo, &tgt_tmp);
 /* XXX: we support only POSIX RT signals are used. */

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