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linux-user: Avoid possible misalignment in host_to_target_siginfo()

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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 <peter.maydell@linaro.org>
Reviewed-by: Laurent Vivier <laurent@vivier.eu>
Signed-off-by: Peter Maydell <riku.voipio@linaro.org>
This commit is contained in:
Peter Maydell 2016-06-13 11:22:05 +01:00 committed by Riku Voipio
parent c728876752
commit 55d72a7eb3
1 changed files with 11 additions and 2 deletions
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13
linux-user/signal.c
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@ -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. */