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[Qemu-devel] [PATCH v2 1/3] linux-user: Avoid possible misalignment in h
From: |
Peter Maydell |
Subject: |
[Qemu-devel] [PATCH v2 1/3] linux-user: Avoid possible misalignment in host_to_target_siginfo() |
Date: |
Thu, 9 Jun 2016 15:09:36 +0100 |
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>
---
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 61c1145..37fb60f 100644
--- a/linux-user/signal.c
+++ b/linux-user/signal.c
@@ -281,6 +281,14 @@ 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
@@ -400,8 +408,9 @@ 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. */
--
1.9.1