From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from pegase1.c-s.fr (pegase1.c-s.fr [93.17.236.30]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 429npT0PSFzF2X0 for ; Thu, 13 Sep 2018 15:51:45 +1000 (AEST) Subject: Re: [PATCH v3] powerpc: Avoid code patching freed init sections To: Michael Neuling , mpe@ellerman.id.au Cc: linuxppc-dev@lists.ozlabs.org, Nicholas Piggin , paulus@ozlabs.org, Haren Myneni , =?UTF-8?Q?Michal_Such=c3=a1nek?= References: <20180913030329.12052-1-mikey@neuling.org> From: Christophe LEROY Message-ID: Date: Thu, 13 Sep 2018 07:51:40 +0200 MIME-Version: 1.0 In-Reply-To: <20180913030329.12052-1-mikey@neuling.org> Content-Type: text/plain; charset=utf-8; format=flowed List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Le 13/09/2018 à 05:03, Michael Neuling a écrit : > This stops us from doing code patching in init sections after they've > been freed. > > In this chain: > kvm_guest_init() -> > kvm_use_magic_page() -> > fault_in_pages_readable() -> > __get_user() -> > __get_user_nocheck() -> > barrier_nospec(); > > We have a code patching location at barrier_nospec() and > kvm_guest_init() is an init function. This whole chain gets inlined, > so when we free the init section (hence kvm_guest_init()), this code > goes away and hence should no longer be patched. > > We seen this as userspace memory corruption when using a memory > checker while doing partition migration testing on powervm (this > starts the code patching post migration via > /sys/kernel/mobility/migration). In theory, it could also happen when > using /sys/kernel/debug/powerpc/barrier_nospec. > > cc: stable@vger.kernel.org # 4.13+ > Signed-off-by: Michael Neuling > > --- > For stable I've marked this as v4.13+ since that's when we refactored > code-patching.c but it could go back even further than that. In > reality though, I think we can only hit this since the first > spectre/meltdown changes. > > v3: > Add init_mem_free flag to avoid potential race. > Feedback from Christophe Leroy: > - use init_section_contains() > - change order of init test for performance > - use pr_debug() > - remove blank line > > v2: > Print when we skip an address > --- > arch/powerpc/include/asm/setup.h | 1 + > arch/powerpc/lib/code-patching.c | 7 +++++++ > arch/powerpc/mm/mem.c | 2 ++ > 3 files changed, 10 insertions(+) > > diff --git a/arch/powerpc/include/asm/setup.h b/arch/powerpc/include/asm/setup.h > index 1a951b0046..4b4522b738 100644 > --- a/arch/powerpc/include/asm/setup.h > +++ b/arch/powerpc/include/asm/setup.h > @@ -9,6 +9,7 @@ extern void ppc_printk_progress(char *s, unsigned short hex); > > extern unsigned int rtas_data; > extern unsigned long long memory_limit; > +extern bool init_mem_free; Calling it init_mem_is_free would be more explicit. Here one might think that it contains the amount of free memory. > extern unsigned long klimit; > extern void *zalloc_maybe_bootmem(size_t size, gfp_t mask); > > diff --git a/arch/powerpc/lib/code-patching.c b/arch/powerpc/lib/code-patching.c > index 850f3b8f4d..dacd6cef92 100644 > --- a/arch/powerpc/lib/code-patching.c > +++ b/arch/powerpc/lib/code-patching.c > @@ -28,6 +28,13 @@ static int __patch_instruction(unsigned int *exec_addr, unsigned int instr, > { > int err; > > + /* Make sure we aren't patching a freed init section */ > + if (init_mem_free && init_section_contains(exec_addr, 4)) { > + pr_debug("Skipping init section patching addr: 0x%lx\n", > + (unsigned long)exec_addr); Using %px instead of %lx would avoid having to cast exec_addr, and then it would fit in one line (in arch/powerpc we accept lines of 90 chars) > + return 0; > + } > + > __put_user_size(instr, patch_addr, 4, err); > if (err) > return err; > diff --git a/arch/powerpc/mm/mem.c b/arch/powerpc/mm/mem.c > index 5c8530d0c6..b9d59e1a83 100644 > --- a/arch/powerpc/mm/mem.c > +++ b/arch/powerpc/mm/mem.c > @@ -63,6 +63,7 @@ > #endif > > unsigned long long memory_limit; > +bool init_mem_free; > > #ifdef CONFIG_HIGHMEM > pte_t *kmap_pte; > @@ -396,6 +397,7 @@ void free_initmem(void) > { > ppc_md.progress = ppc_printk_progress; > mark_initmem_nx(); > + init_mem_free = true; > free_initmem_default(POISON_FREE_INITMEM); > } > > Reviewed-by: Christophe Leroy Christophe