From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: From: Jeff Moyer To: Matthew Wilcox Cc: Alexander Viro , Benjamin LaHaise , Andrew Morton , Kees Cook , linux-fsdevel@vger.kernel.org, linux-aio@kvack.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Dan Carpenter Subject: Re: [PATCH] aio: Convert ioctx_table to XArray References: <20181128183531.5139-1-willy@infradead.org> Date: Tue, 11 Dec 2018 12:21:52 -0500 In-Reply-To: (Jeff Moyer's message of "Thu, 06 Dec 2018 17:26:33 -0500") Message-ID: MIME-Version: 1.0 Content-Type: text/plain Sender: owner-linux-mm@kvack.org List-ID: Jeff Moyer writes: > Jeff Moyer writes: > >> Matthew Wilcox writes: >> >>> This custom resizing array was vulnerable to a Spectre attack (speculating >>> off the end of an array to a user-controlled offset). The XArray is >>> not vulnerable to Spectre as it always masks its lookups to be within >>> the bounds of the array. >> >> I'm not a big fan of completely re-writing the code to fix this. Isn't >> the below patch sufficient? > > Too quick on the draw. Here's a patch that compiles. ;-) Hi, Matthew, I'm going to submit this version formally. If you're interested in converting the ioctx_table to xarray, you can do that separately from a security fix. I would include a performance analysis with that patch, though. The idea of using a radix tree for the ioctx table was discarded due to performance reasons--see commit db446a08c23d5 ("aio: convert the ioctx list to table lookup v3"). I suspect using the xarray will perform similarly. Cheers, Jeff > diff --git a/fs/aio.c b/fs/aio.c > index 97f983592925..aac9659381d2 100644 > --- a/fs/aio.c > +++ b/fs/aio.c > @@ -45,6 +45,7 @@ > > #include > #include > +#include > > #include "internal.h" > > @@ -1038,6 +1039,7 @@ static struct kioctx *lookup_ioctx(unsigned long ctx_id) > if (!table || id >= table->nr) > goto out; > > + id = array_index_nospec(id, table->nr); > ctx = rcu_dereference(table->table[id]); > if (ctx && ctx->user_id == ctx_id) { > if (percpu_ref_tryget_live(&ctx->users)) > > -- > To unsubscribe, send a message with 'unsubscribe linux-aio' in > the body to majordomo@kvack.org. For more info on Linux AIO, > see: http://www.kvack.org/aio/ > Don't email: aart@kvack.org