[linux] 02/02: [powerpc*] Fix illegal TM state in signal handler

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carnil pushed a commit to branch sid
in repository linux.

commit fba37066c705ed8fa120ec6e7845096b53b71e2f
Author: Salvatore Bonaccorso <carnil at debian.org>
Date:   Wed Oct 11 07:56:11 2017 +0200

    [powerpc*] Fix illegal TM state in signal handler
---
 debian/changelog                                   |  1 +
 ...tm-Fix-illegal-TM-state-in-signal-handler.patch | 62 ++++++++++++++++++++++
 debian/patches/series                              |  1 +
 3 files changed, 64 insertions(+)

diff --git a/debian/changelog b/debian/changelog
index 24aa465..c259cf0 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 <ben at decadent.org.uk>  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 0000000..083cbbe
--- /dev/null
+++ b/debian/patches/bugfix/all/powerpc-tm-Fix-illegal-TM-state-in-signal-handler.patch
@@ -0,0 +1,62 @@
+From: Gustavo Romero <gromero at linux.vnet.ibm.com>
+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 at vger.kernel.org # v4.9+
+Signed-off-by: Gustavo Romero <gromero at linux.vnet.ibm.com>
+Signed-off-by: Breno Leitao <leitao at debian.org>
+Signed-off-by: Cyril Bur <cyrilbur at gmail.com>
+Signed-off-by: Michael Ellerman <mpe at ellerman.id.au>
+---
+ 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 badc6df..9a97407 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

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