From: Michael Neuling mikey@neuling.org
commit 1da4a0272c5469169f78cd76cf175ff984f52f06 upstream.
__get_user_atomic_128_aligned() stores to kaddr using stvx which is a VMX store instruction, hence kaddr must be 16 byte aligned otherwise the store won't occur as expected.
Unfortunately when we call __get_user_atomic_128_aligned() in p9_hmi_special_emu(), the buffer we pass as kaddr (ie. vbuf) isn't guaranteed to be 16B aligned. This means that the write to vbuf in __get_user_atomic_128_aligned() has the bottom bits of the address truncated. This results in other local variables being overwritten. Also vbuf will not contain the correct data which results in the userspace emulation being wrong and hence undetected user data corruption.
In the past we've been mostly lucky as vbuf has ended up aligned but this is fragile and isn't always true. CONFIG_STACKPROTECTOR in particular can change the stack arrangement enough that our luck runs out.
This issue only occurs on POWER9 Nimbus <= DD2.1 bare metal.
The fix is to align vbuf to a 16 byte boundary.
Fixes: 5080332c2c89 ("powerpc/64s: Add workaround for P9 vector CI load issue") Cc: stable@vger.kernel.org # v4.15+ Signed-off-by: Michael Neuling mikey@neuling.org Signed-off-by: Michael Ellerman mpe@ellerman.id.au Link: https://lore.kernel.org/r/20201013043741.743413-1-mikey@neuling.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- arch/powerpc/kernel/traps.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
--- a/arch/powerpc/kernel/traps.c +++ b/arch/powerpc/kernel/traps.c @@ -889,7 +889,7 @@ static void p9_hmi_special_emu(struct pt { unsigned int ra, rb, t, i, sel, instr, rc; const void __user *addr; - u8 vbuf[16], *vdst; + u8 vbuf[16] __aligned(16), *vdst; unsigned long ea, msr, msr_mask; bool swap;