From fba37066c705ed8fa120ec6e7845096b53b71e2f Mon Sep 17 00:00:00 2001 From: Salvatore Bonaccorso Date: Wed, 11 Oct 2017 07:56:11 +0200 Subject: [PATCH] [powerpc*] Fix illegal TM state in signal handler --- debian/changelog | 1 + ...x-illegal-TM-state-in-signal-handler.patch | 62 +++++++++++++++++++ debian/patches/series | 1 + 3 files changed, 64 insertions(+) create mode 100644 debian/patches/bugfix/all/powerpc-tm-Fix-illegal-TM-state-in-signal-handler.patch diff --git a/debian/changelog b/debian/changelog index 24aa4657d..c259cf052 100644 --- a/debian/changelog +++ b/debian/changelog @@ -8,6 +8,7 @@ linux (4.13.4-2) UNRELEASED; urgency=medium (CVE-2017-0786) * [powerpc*] Use emergency stack for kernel TM Bad Thing program (CVE-2017-1000255) + * [powerpc*] Fix illegal TM state in signal handler -- Ben Hutchings Wed, 04 Oct 2017 23:14:54 +0100 diff --git a/debian/patches/bugfix/all/powerpc-tm-Fix-illegal-TM-state-in-signal-handler.patch b/debian/patches/bugfix/all/powerpc-tm-Fix-illegal-TM-state-in-signal-handler.patch new file mode 100644 index 000000000..083cbbee7 --- /dev/null +++ b/debian/patches/bugfix/all/powerpc-tm-Fix-illegal-TM-state-in-signal-handler.patch @@ -0,0 +1,62 @@ +From: Gustavo Romero +Date: Tue, 22 Aug 2017 17:20:09 -0400 +Subject: powerpc/tm: Fix illegal TM state in signal handler +Origin: https://git.kernel.org/linus/044215d145a7a8a60ffa8fdc859d110a795fa6ea + +Currently it's possible that on returning from the signal handler +through the restore_tm_sigcontexts() code path (e.g. from a signal +caught due to a `trap` instruction executed in the middle of an HTM +block, or a deliberately constructed sigframe) an illegal TM state +(like TS=10 TM=0, i.e. "T0") is set in SRR1 and when `rfid` sets +implicitly the MSR register from SRR1 register on return to userspace +it causes a TM Bad Thing exception. + +That illegal state can be set (a) by a malicious user that disables +the TM bit by tweaking the bits in uc_mcontext before returning from +the signal handler or (b) by a sufficient number of context switches +occurring such that the load_tm counter overflows and TM is disabled +whilst in the signal handler. + +This commit fixes the illegal TM state by ensuring that TM bit is +always enabled before we return from restore_tm_sigcontexts(). A small +comment correction is made as well. + +Fixes: 5d176f751ee3 ("powerpc: tm: Enable transactional memory (TM) lazily for userspace") +Cc: stable@vger.kernel.org # v4.9+ +Signed-off-by: Gustavo Romero +Signed-off-by: Breno Leitao +Signed-off-by: Cyril Bur +Signed-off-by: Michael Ellerman +--- + arch/powerpc/kernel/signal_64.c | 13 ++++++++++++- + 1 file changed, 12 insertions(+), 1 deletion(-) + +diff --git a/arch/powerpc/kernel/signal_64.c b/arch/powerpc/kernel/signal_64.c +index c83c115858c1..b2c002993d78 100644 +--- a/arch/powerpc/kernel/signal_64.c ++++ b/arch/powerpc/kernel/signal_64.c +@@ -452,9 +452,20 @@ static long restore_tm_sigcontexts(struct task_struct *tsk, + if (MSR_TM_RESV(msr)) + return -EINVAL; + +- /* pull in MSR TM from user context */ ++ /* pull in MSR TS bits from user context */ + regs->msr = (regs->msr & ~MSR_TS_MASK) | (msr & MSR_TS_MASK); + ++ /* ++ * Ensure that TM is enabled in regs->msr before we leave the signal ++ * handler. It could be the case that (a) user disabled the TM bit ++ * through the manipulation of the MSR bits in uc_mcontext or (b) the ++ * TM bit was disabled because a sufficient number of context switches ++ * happened whilst in the signal handler and load_tm overflowed, ++ * disabling the TM bit. In either case we can end up with an illegal ++ * TM state leading to a TM Bad Thing when we return to userspace. ++ */ ++ regs->msr |= MSR_TM; ++ + /* pull in MSR LE from user context */ + regs->msr = (regs->msr & ~MSR_LE) | (msr & MSR_LE); + +-- +2.11.0 + diff --git a/debian/patches/series b/debian/patches/series index badc6df9f..9a974070f 100644 --- a/debian/patches/series +++ b/debian/patches/series @@ -121,6 +121,7 @@ bugfix/x86/kvm-vmx-do-not-bug-on-out-of-bounds-guest-irq.patch bugfix/all/fix-infoleak-in-waitid-2.patch bugfix/all/brcmfmac-add-length-check-in-brcmf_cfg80211_escan_ha.patch bugfix/all/powerpc-64s-Use-emergency-stack-for-kernel-TM-Bad-Th.patch +bugfix/all/powerpc-tm-Fix-illegal-TM-state-in-signal-handler.patch # Fix exported symbol versions bugfix/alpha/alpha-restore-symbol-versions-for-symbols-exported-f.patch