From patchwork Tue Mar 3 12:59:49 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Michael Ellerman X-Patchwork-Id: 1248355 Return-Path: X-Original-To: patchwork-incoming@ozlabs.org Delivered-To: patchwork-incoming@ozlabs.org Received: from lists.ozlabs.org (lists.ozlabs.org [IPv6:2401:3900:2:1::3]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits)) (No client certificate requested) by ozlabs.org (Postfix) with ESMTPS id 48WxzL3WZjz9sRN for ; Wed, 4 Mar 2020 00:03:58 +1100 (AEDT) Authentication-Results: ozlabs.org; dmarc=none (p=none dis=none) header.from=ellerman.id.au Authentication-Results: ozlabs.org; dkim=fail reason="signature verification failed" (2048-bit key; unprotected) header.d=ellerman.id.au header.i=@ellerman.id.au header.a=rsa-sha256 header.s=201909 header.b=TfUJOEvv; dkim-atps=neutral Received: from lists.ozlabs.org (lists.ozlabs.org [IPv6:2401:3900:2:1::3]) by lists.ozlabs.org (Postfix) with ESMTP id 48WxzK73VGzDqTF for ; Wed, 4 Mar 2020 00:03:57 +1100 (AEDT) X-Original-To: linuxppc-dev@lists.ozlabs.org Delivered-To: linuxppc-dev@lists.ozlabs.org Received: from ozlabs.org (bilbo.ozlabs.org [IPv6:2401:3900:2:1::2]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 48Wxth2gbpzDqKs for ; Tue, 3 Mar 2020 23:59:56 +1100 (AEDT) Authentication-Results: lists.ozlabs.org; dmarc=none (p=none dis=none) header.from=ellerman.id.au Authentication-Results: lists.ozlabs.org; dkim=pass (2048-bit key; unprotected) header.d=ellerman.id.au header.i=@ellerman.id.au header.a=rsa-sha256 header.s=201909 header.b=TfUJOEvv; dkim-atps=neutral Received: by ozlabs.org (Postfix) id 48Wxtg5lP0z9sPg; Tue, 3 Mar 2020 23:59:55 +1100 (AEDT) Delivered-To: linuxppc-dev@ozlabs.org Received: by ozlabs.org (Postfix, from userid 1034) id 48Wxtg4bZXz9sRR; Tue, 3 Mar 2020 23:59:55 +1100 (AEDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=ellerman.id.au; s=201909; t=1583240395; bh=Ycez99IX8MsJIhG/ziIKviG9V19ODMBs3uzZQUM6R04=; h=From:To:Cc:Subject:Date:From; b=TfUJOEvvyUskVXS4bVm1qS31f6HQlO0Z7xDu8mrPwsOmdImMxjE/kQ5Bj+WRxd4gm oWa3kebtLUuzBGWg4tiAoBVbjPxySqVrjGCAt6fN0QB+YGDAuD55Iz2YSzxKsr5GJU EFlxPgEINlVjB1RANI1vB5VjTn9V06WNqOXZ3E6Ev/4C0Ms8g2/ZX/nnRWK1wpUYB8 nLVr78DyLS5WzjkhK+1QV3X23EdW0JV0QqPOKFuticIIMcHCFXGzMSOMgvdjmxLjsl uBKHYJ3snWk2HAxaf1GoVn1AVDuArlEUUWqOQ2APeN4rvXKa8k1Jcfs3YflzqEbSie M6ffnQpUFwC+w== From: Michael Ellerman To: linuxppc-dev@ozlabs.org Subject: [PATCH] powerpc/mm: Fix missing KUAP disable in flush_coherent_icache() Date: Tue, 3 Mar 2020 23:59:49 +1100 Message-Id: <20200303125949.27172-1-mpe@ellerman.id.au> X-Mailer: git-send-email 2.21.1 MIME-Version: 1.0 X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: linuxppc-dev-bounces+patchwork-incoming=ozlabs.org@lists.ozlabs.org Sender: "Linuxppc-dev" We received a report of strange kernel faults which turned out to be due to a missing KUAP disable in flush_coherent_icache() called from flush_icache_range(). The fault looks like: Kernel attempted to access user page (7fffc30d9c00) - exploit attempt? (uid: 1009) BUG: Unable to handle kernel data access on read at 0x7fffc30d9c00 Faulting instruction address: 0xc00000000007232c Oops: Kernel access of bad area, sig: 11 [#1] LE PAGE_SIZE=64K MMU=Radix SMP NR_CPUS=2048 NUMA PowerNV CPU: 35 PID: 5886 Comm: sigtramp Not tainted 5.6.0-rc2-gcc-8.2.0-00003-gfc37a1632d40 #79 NIP: c00000000007232c LR: c00000000003b7fc CTR: 0000000000000000 REGS: c000001e11093940 TRAP: 0300 Not tainted (5.6.0-rc2-gcc-8.2.0-00003-gfc37a1632d40) MSR: 900000000280b033 CR: 28000884 XER: 00000000 CFAR: c0000000000722fc DAR: 00007fffc30d9c00 DSISR: 08000000 IRQMASK: 0 GPR00: c00000000003b7fc c000001e11093bd0 c0000000023ac200 00007fffc30d9c00 GPR04: 00007fffc30d9c18 0000000000000000 c000001e11093bd4 0000000000000000 GPR08: 0000000000000000 0000000000000001 0000000000000000 c000001e1104ed80 GPR12: 0000000000000000 c000001fff6ab380 c0000000016be2d0 4000000000000000 GPR16: c000000000000000 bfffffffffffffff 0000000000000000 0000000000000000 GPR20: 00007fffc30d9c00 00007fffc30d8f58 00007fffc30d9c18 00007fffc30d9c20 GPR24: 00007fffc30d9c18 0000000000000000 c000001e11093d90 c000001e1104ed80 GPR28: c000001e11093e90 0000000000000000 c0000000023d9d18 00007fffc30d9c00 NIP flush_icache_range+0x5c/0x80 LR handle_rt_signal64+0x95c/0xc2c Call Trace: 0xc000001e11093d90 (unreliable) handle_rt_signal64+0x93c/0xc2c do_notify_resume+0x310/0x430 ret_from_except_lite+0x70/0x74 Instruction dump: 409e002c 7c0802a6 3c62ff31 3863f6a0 f8010080 48195fed 60000000 48fe4c8d 60000000 e8010080 7c0803a6 7c0004ac <7c00ffac> 7c0004ac 4c00012c 38210070 This path through handle_rt_signal64() to setup_trampoline() and flush_icache_range() is only triggered by 64-bit processes that have unmapped their VDSO, which is rare. flush_icache_range() takes a range of addresses to flush. In flush_coherent_icache() we implement an optimisation for CPUs where we know we don't actually have to flush the whole range, we just need to do a single icbi. However we still execute the icbi on the user address of the start of the range we're flushing. On CPUs that also implement KUAP (Power9) that leads to the spurious fault above. We should be able to pass any address, including a kernel address, to the icbi on these CPUs, which would avoid any interaction with KUAP. But I don't want to make that change in a bug fix, just in case it surfaces some strange behaviour on some CPU. So for now just disable KUAP around the icbi. Note the icbi is treated as a load, so we allow read access, not write as you'd expect. Fixes: 890274c2dc4c ("powerpc/64s: Implement KUAP for Radix MMU") Cc: stable@vger.kernel.org # v5.2+ Signed-off-by: Michael Ellerman --- arch/powerpc/mm/mem.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/arch/powerpc/mm/mem.c b/arch/powerpc/mm/mem.c index ef7b1119b2e2..184850d9d000 100644 --- a/arch/powerpc/mm/mem.c +++ b/arch/powerpc/mm/mem.c @@ -373,7 +373,9 @@ static inline bool flush_coherent_icache(unsigned long addr) */ if (cpu_has_feature(CPU_FTR_COHERENT_ICACHE)) { mb(); /* sync */ + allow_read_from_user((void *)addr, 4); icbi((void *)addr); + prevent_read_from_user((void *)addr, 4); mb(); /* sync */ isync(); return true;