From: James Hogan <james.hogan@xxxxxxxxxx> This patch has been added to the 3.18 stable tree. If you have any objections, please let us know. =============== [ Upstream commit 3aff47c062b944a5e1f9af56a37a23f5295628fc ] When EVA is enabled, flush the Return Prediction Stack (RPS) present on some MIPS cores on entry to the kernel from user mode. This is important specifically for interAptiv with EVA enabled, otherwise kernel mode RPS mispredicts may trigger speculative fetches of user return addresses, which may be sensitive in the kernel address space due to EVA's overlapping user/kernel address spaces. Signed-off-by: James Hogan <james.hogan@xxxxxxxxxx> Cc: Ralf Baechle <ralf@xxxxxxxxxxxxxx> Cc: Markos Chandras <markos.chandras@xxxxxxxxxx> Cc: Leonid Yegoshin <leonid.yegoshin@xxxxxxxxxx> Cc: linux-mips@xxxxxxxxxxxxxx Cc: <stable@xxxxxxxxxxxxxxx> # 3.15.x- Patchwork: https://patchwork.linux-mips.org/patch/10812/ Signed-off-by: Ralf Baechle <ralf@xxxxxxxxxxxxxx> Signed-off-by: Sasha Levin <sasha.levin@xxxxxxxxxx> --- arch/mips/include/asm/stackframe.h | 25 +++++++++++++++++++++++++ 1 file changed, 25 insertions(+) diff --git a/arch/mips/include/asm/stackframe.h b/arch/mips/include/asm/stackframe.h index b188c79..0562a24 100644 --- a/arch/mips/include/asm/stackframe.h +++ b/arch/mips/include/asm/stackframe.h @@ -152,6 +152,31 @@ .set noreorder bltz k0, 8f move k1, sp +#ifdef CONFIG_EVA + /* + * Flush interAptiv's Return Prediction Stack (RPS) by writing + * EntryHi. Toggling Config7.RPS is slower and less portable. + * + * The RPS isn't automatically flushed when exceptions are + * taken, which can result in kernel mode speculative accesses + * to user addresses if the RPS mispredicts. That's harmless + * when user and kernel share the same address space, but with + * EVA the same user segments may be unmapped to kernel mode, + * even containing sensitive MMIO regions or invalid memory. + * + * This can happen when the kernel sets the return address to + * ret_from_* and jr's to the exception handler, which looks + * more like a tail call than a function call. If nested calls + * don't evict the last user address in the RPS, it will + * mispredict the return and fetch from a user controlled + * address into the icache. + * + * More recent EVA-capable cores with MAAR to restrict + * speculative accesses aren't affected. + */ + MFC0 k0, CP0_ENTRYHI + MTC0 k0, CP0_ENTRYHI +#endif .set reorder /* Called from user mode, new stack. */ get_saved_sp -- 2.1.4
