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author | Gustavo Romero <gromero@linux.vnet.ibm.com> | 2017-12-31 18:20:45 -0500 |
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committer | Michael Ellerman <mpe@ellerman.id.au> | 2018-01-22 05:48:36 +1100 |
commit | 1c200e63d055ec0125e44a5e386b9b78aada7eb3 (patch) | |
tree | 797e6edb79c02707990f056dc1b91384ba7edf0a /arch/powerpc/kernel/signal_64.c | |
parent | b6d34eb4d280c893d0f442f4b9e039d73e3db420 (diff) | |
download | linux-1c200e63d055ec0125e44a5e386b9b78aada7eb3.tar.bz2 |
powerpc/tm: Fix endianness flip on trap
Currently it's possible that a thread on PPC64 LE has its endianness
flipped inadvertently to Big-Endian resulting in a crash once the process
is back from the signal handler.
If giveup_all() is called when regs->msr has the bits MSR.FP and MSR.VEC
disabled (and hence MSR.VSX disabled too) it returns without calling
check_if_tm_restore_required() which copies regs->msr to ckpt_regs->msr if
the process caught a signal whilst in transactional mode. Then once in
setup_tm_sigcontexts() MSR from ckpt_regs.msr is used, but since
check_if_tm_restore_required() was not called previuosly, gp_regs[PT_MSR]
gets a copy of invalid MSR bits as MSR in ckpt_regs was not updated from
regs->msr and so is zeroed. Later when leaving the signal handler once in
sys_rt_sigreturn() the TS bits of gp_regs[PT_MSR] are checked to determine
if restore_tm_sigcontexts() must be called to pull in the correct MSR state
into the user context. Because TS bits are zeroed
restore_tm_sigcontexts() is never called and MSR restored from the user
context on returning from the signal handler has the MSR.LE (the endianness
bit) forced to zero (Big-Endian). That leads, for instance, to 'nop' being
treated as an illegal instruction in the following sequence:
tbegin.
beq 1f
trap
tend.
1: nop
on PPC64 LE machines and the process dies just after returning from the
signal handler.
PPC64 BE is also affected but in a subtle way since forcing Big-Endian on
a BE machine does not change the endianness.
This commit fixes the issue described above by ensuring that once in
setup_tm_sigcontexts() the MSR used is from regs->msr instead of from
ckpt_regs->msr and by ensuring that we pull in only the MSR.FP, MSR.VEC,
and MSR.VSX bits from ckpt_regs->msr.
The fix was tested both on LE and BE machines and no regression regarding
the powerpc/tm selftests was observed.
Signed-off-by: Gustavo Romero <gromero@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Diffstat (limited to 'arch/powerpc/kernel/signal_64.c')
-rw-r--r-- | arch/powerpc/kernel/signal_64.c | 8 |
1 files changed, 7 insertions, 1 deletions
diff --git a/arch/powerpc/kernel/signal_64.c b/arch/powerpc/kernel/signal_64.c index 2705fba544ad..720117690822 100644 --- a/arch/powerpc/kernel/signal_64.c +++ b/arch/powerpc/kernel/signal_64.c @@ -210,7 +210,7 @@ static long setup_tm_sigcontexts(struct sigcontext __user *sc, elf_vrreg_t __user *tm_v_regs = sigcontext_vmx_regs(tm_sc); #endif struct pt_regs *regs = tsk->thread.regs; - unsigned long msr = tsk->thread.ckpt_regs.msr; + unsigned long msr = tsk->thread.regs->msr; long err = 0; BUG_ON(tsk != current); @@ -219,6 +219,12 @@ static long setup_tm_sigcontexts(struct sigcontext __user *sc, WARN_ON(tm_suspend_disabled); + /* Restore checkpointed FP, VEC, and VSX bits from ckpt_regs as + * it contains the correct FP, VEC, VSX state after we treclaimed + * the transaction and giveup_all() was called on reclaiming. + */ + msr |= tsk->thread.ckpt_regs.msr & (MSR_FP | MSR_VEC | MSR_VSX); + /* Remove TM bits from thread's MSR. The MSR in the sigcontext * just indicates to userland that we were doing a transaction, but we * don't want to return in transactional state. This also ensures |