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| author | Michael Ellerman <mpe@ellerman.id.au> | 2020-03-31 13:47:19 +0200 |
|---|---|---|
| committer | Michael Ellerman <mpe@ellerman.id.au> | 2020-04-01 04:42:00 +0200 |
| commit | c7def7fbdeaa25feaa19caf4a27c5d10bd8789e4 (patch) | |
| tree | 6ddfd3b8806e7f0aaabb8a8d931574435c1c8ec6 /arch/powerpc | |
| parent | powerpc/64: Avoid isync in flush_dcache_range() (diff) | |
| download | linux-c7def7fbdeaa25feaa19caf4a27c5d10bd8789e4.tar.xz linux-c7def7fbdeaa25feaa19caf4a27c5d10bd8789e4.zip | |
powerpc/64/tm: Don't let userspace set regs->trap via sigreturn
In restore_tm_sigcontexts() we take the trap value directly from the
user sigcontext with no checking:
err |= __get_user(regs->trap, &sc->gp_regs[PT_TRAP]);
This means we can be in the kernel with an arbitrary regs->trap value.
Although that's not immediately problematic, there is a risk we could
trigger one of the uses of CHECK_FULL_REGS():
#define CHECK_FULL_REGS(regs) BUG_ON(regs->trap & 1)
It can also cause us to unnecessarily save non-volatile GPRs again in
save_nvgprs(), which shouldn't be problematic but is still wrong.
It's also possible it could trick the syscall restart machinery, which
relies on regs->trap not being == 0xc00 (see 9a81c16b5275 ("powerpc:
fix double syscall restarts")), though I haven't been able to make
that happen.
Finally it doesn't match the behaviour of the non-TM case, in
restore_sigcontext() which zeroes regs->trap.
So change restore_tm_sigcontexts() to zero regs->trap.
This was discovered while testing Nick's upcoming rewrite of the
syscall entry path. In that series the call to save_nvgprs() prior to
signal handling (do_notify_resume()) is removed, which leaves the
low-bit of regs->trap uncleared which can then trigger the FULL_REGS()
WARNs in setup_tm_sigcontexts().
Fixes: 2b0a576d15e0 ("powerpc: Add new transactional memory state to the signal context")
Cc: stable@vger.kernel.org # v3.9+
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20200401023836.3286664-1-mpe@ellerman.id.au
Diffstat (limited to 'arch/powerpc')
| -rw-r--r-- | arch/powerpc/kernel/signal_64.c | 4 |
1 files changed, 3 insertions, 1 deletions
diff --git a/arch/powerpc/kernel/signal_64.c b/arch/powerpc/kernel/signal_64.c index 84ed2e77ef9c..adfde59cf4ba 100644 --- a/arch/powerpc/kernel/signal_64.c +++ b/arch/powerpc/kernel/signal_64.c @@ -473,8 +473,10 @@ static long restore_tm_sigcontexts(struct task_struct *tsk, err |= __get_user(tsk->thread.ckpt_regs.ccr, &sc->gp_regs[PT_CCR]); + /* Don't allow userspace to set the trap value */ + regs->trap = 0; + /* These regs are not checkpointed; they can go in 'regs'. */ - err |= __get_user(regs->trap, &sc->gp_regs[PT_TRAP]); err |= __get_user(regs->dar, &sc->gp_regs[PT_DAR]); err |= __get_user(regs->dsisr, &sc->gp_regs[PT_DSISR]); err |= __get_user(regs->result, &sc->gp_regs[PT_RESULT]); |