From patchwork Mon Apr 17 12:13:57 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Andrew Cooper X-Patchwork-Id: 13213750 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from lists.xenproject.org (lists.xenproject.org [192.237.175.120]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 4E1AAC77B77 for ; Mon, 17 Apr 2023 12:14:38 +0000 (UTC) Received: from list by lists.xenproject.org with outflank-mailman.522033.811175 (Exim 4.92) (envelope-from ) id 1poNkb-0001HN-0F; Mon, 17 Apr 2023 12:14:29 +0000 X-Outflank-Mailman: Message body and most headers restored to incoming version Received: by outflank-mailman (output) from mailman id 522033.811175; Mon, 17 Apr 2023 12:14:28 +0000 Received: from localhost ([127.0.0.1] helo=lists.xenproject.org) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1poNka-0001HE-TZ; Mon, 17 Apr 2023 12:14:28 +0000 Received: by outflank-mailman (input) for mailman id 522033; Mon, 17 Apr 2023 12:14:27 +0000 Received: from se1-gles-flk1-in.inumbo.com ([94.247.172.50] helo=se1-gles-flk1.inumbo.com) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1poNkY-0000xC-Vw for xen-devel@lists.xenproject.org; Mon, 17 Apr 2023 12:14:26 +0000 Received: from esa6.hc3370-68.iphmx.com (esa6.hc3370-68.iphmx.com [216.71.155.175]) by se1-gles-flk1.inumbo.com (Halon) with ESMTPS id 6479c75b-dd19-11ed-8611-37d641c3527e; Mon, 17 Apr 2023 14:14:25 +0200 (CEST) X-BeenThere: xen-devel@lists.xenproject.org List-Id: Xen developer discussion List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Errors-To: xen-devel-bounces@lists.xenproject.org Precedence: list Sender: "Xen-devel" X-Inumbo-ID: 6479c75b-dd19-11ed-8611-37d641c3527e DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=citrix.com; s=securemail; t=1681733664; h=from:to:cc:subject:date:message-id:in-reply-to: references:mime-version:content-transfer-encoding; bh=Ew+rB9d1GFmavjWRsz8+3kGUcmwxQ2u2fM4aYYZINb4=; b=e/ow2rp1E2xrM7btd1qpiSEkma/y2KWlQ64rBQJRF4SoeAY681cceWwZ z6QNGkuXfcjuNYamDiME3LQpYSydCmhNuNCzga+XqZxzn5CD8bnFNM260 8vmSsADNpDn6E+R9adlyUZz56L6SDgl6wymQqZp1wYpNzm055MrCFMpvJ s=; Authentication-Results: esa6.hc3370-68.iphmx.com; dkim=none (message not signed) header.i=none X-SBRS: 4.0 X-MesageID: 105144452 X-Ironport-Server: esa6.hc3370-68.iphmx.com X-Remote-IP: 162.221.156.123 X-Policy: $RELAYED IronPort-Data: A9a23:nPoUKaJ8dejJkM8MFE+RoJUlxSXFcZb7ZxGr2PjKsXjdYENSgTFWm GpOWGnSOvyLM2f8LYx1bY7l/RhU7ZWDz9dqQQVlqX01Q3x08seUXt7xwmUcnc+xBpaaEB84t ZV2hv3odp1coqr0/0/1WlTZhSAgk/rOHvykU7Ss1hlZHWdMUD0mhQ9oh9k3i4tphcnRKw6Ws Jb5rta31GWNglaYCUpJrfPSwP9TlK6q4mhA4gVhPakjUGL2zBH5MrpOfcldEFOgKmVkNrbSb /rOyri/4lTY838FYj9yuu+mGqGiaue60Tmm0hK6aYD76vRxjnVaPpIAHOgdcS9qZwChxLid/ jnvWauYEm/FNoWU8AgUvoIx/ytWZcWq85efSZSzXFD6I+QrvBIAzt03ZHzaM7H09c5FRkFL/ 9E5dglONDvb3e+H8oPrds5F05FLwMnDZOvzu1llxDDdS/0nXYrCU+PB4towMDUY354UW6yEP oxANGQpNU6bC/FMEg5/5JYWteGknHTgNRZfr0qYv/Ef6GnP1g1hlrPqNbI5f/TTHZgMwhrE+ ziuE2LRITIcMfiT4xW80XOW3M3UunuiW8UiPejtnhJtqALKnTFCYPEMbnOrrP/8hkOgVtZ3L 00P5jFovaU07FasTNT2Q1u/unHslh0bXcBZH6sl6QWO4q3O6g2dCy4PSTspVTA9nJZoH3pwj AbPxo63Q2U169V5VE5x6J+m6hO3MwU0c1ZBPwRcFwY00eiznKYa20enoslYLEKlsjHkMWiuk 2nW93lj1ul7Yd0jjPviow2e6964jt2QF1NuuF2KNo6wxlkhDLNJcbBE/rQyARxoCI+CBmeMs 3Ef8yR1xLBfVMrd/MBhrQhkIV1I2xpmGGeG6bKXN8N9nwlBAlb6FWyq3BlwJV1yLuEPciLzb UnYtGt5vcEDZSX1NfcqPt3pV6zGKJQM8vy8D5jpgidmOMAtJGdrAgk1DaJv44wduBd1yvxuU XtqWc2tEWwbGcxa8dZCfM9EieVD7nlnlQvuqWXTk0zPPUy2OCTEFt/o8TKmMogE0U9ziF+Nq 4wAbJPalUw3vS+XSnC/zLP/5GsidRATba0aYeQOJoZv/iIO9LkdNsLs IronPort-HdrOrdr: A9a23:iUwiKaEgP1UZ1KT/pLqELMeALOsnbusQ8zAXPiBKJCC9E/bo8v xG+c5w6faaslkssR0b9+xoW5PwI080l6QU3WB5B97LMDUO0FHCEGgI1/qA/9SPIUzDHu4279 YbT0B9YueAcGSTW6zBkXWF+9VL+qj5zEix792uq0uE1WtRGtldBwESMHf9LmRGADNoKLAeD5 Sm6s9Ot1ObCA8qhpTSPAhiYwDbzee77a7bXQ== X-Talos-CUID: 9a23:Oe38jWhWonu2y6/LPwG1wDm0pzJuQDr9yX39AhGBSjxCEOeYeG2hqJ9Dup87 X-Talos-MUID: 9a23:qp6IBwkdYm03/lQX3dkJdnpBF8Ftx6iEJ3kukK9cmdKjbXVzfAe02WE= X-IronPort-AV: E=Sophos;i="5.99,204,1677560400"; d="scan'208";a="105144452" From: Andrew Cooper To: Xen-devel CC: Andrew Cooper , Konrad Rzeszutek Wilk , Ross Lagerwall Subject: [PATCH v2 3/3] xen/livepatch: Fix .altinstructions safety checks Date: Mon, 17 Apr 2023 13:13:57 +0100 Message-ID: <20230417121357.3738919-4-andrew.cooper3@citrix.com> X-Mailer: git-send-email 2.30.2 In-Reply-To: <20230417121357.3738919-1-andrew.cooper3@citrix.com> References: <20230417121357.3738919-1-andrew.cooper3@citrix.com> MIME-Version: 1.0 The prior check has && vs || mixups, making it tautologically false and thus providing no safety at all. There are boundary errors too. First start with a comment describing how the .altinstructions and .altinstr_replacement sections interact, and perform suitable cross-checking. Second, rewrite the alt_instr loop entirely from scratch. Origin sites have non-zero size, and must be fully contained within the livepatches .text section(s). Any non-zero sized replacements must be fully contained within the .altinstr_replacement section. Fixes: f8a10174e8b1 ("xsplice: Add support for alternatives") Signed-off-by: Andrew Cooper Reviewed-by: Ross Lagerwall --- CC: Konrad Rzeszutek Wilk CC: Ross Lagerwall v2: * Rebase over prior patches to keep the ARM build working * Tweak commit message and comments for clarity As a further observation, .altinstr_replacement shouldn't survive beyond its use in apply_alternatives(), but the disp32 relative references (for x86 at least) in alt_instr force .altinstr_replacement to be close to the payload while being applied. --- xen/common/livepatch.c | 68 ++++++++++++++++++++++++++++++++---- xen/include/xen/elfstructs.h | 2 ++ 2 files changed, 64 insertions(+), 6 deletions(-) diff --git a/xen/common/livepatch.c b/xen/common/livepatch.c index c10ab1f374e0..004b5a436569 100644 --- a/xen/common/livepatch.c +++ b/xen/common/livepatch.c @@ -803,28 +803,84 @@ static int prepare_payload(struct payload *payload, if ( sec ) { #ifdef CONFIG_HAS_ALTERNATIVE + /* + * (As of April 2023), Alternatives are formed of: + * - An .altinstructions section with an array of struct alt_instr's. + * - An .altinstr_replacement section containing instructions. + * + * An individual alt_instr contains: + * - An orig reference, pointing into .text with a nonzero length + * - A repl reference, pointing into .altinstr_replacement + * + * It is legal to have zero-length replacements, meaning it is legal + * for the .altinstr_replacement section to be empty too. An + * implementation detail means that a zero-length replacement's repl + * reference will still be in the .altinstr_replacement section. + */ + const struct livepatch_elf_sec *repl_sec; struct alt_instr *a, *start, *end; if ( !section_ok(elf, sec, sizeof(*a)) ) return -EINVAL; + /* Tolerate an empty .altinstructions section... */ + if ( sec->sec->sh_size == 0 ) + goto alt_done; + + /* ... but otherwise, there needs to be something to alter... */ + if ( payload->text_size == 0 ) + { + printk(XENLOG_ERR LIVEPATCH "%s Alternatives provided, but no .text\n", + elf->name); + return -EINVAL; + } + + /* ... and something to be altered to. */ + repl_sec = livepatch_elf_sec_by_name(elf, ".altinstr_replacement"); + if ( !repl_sec ) + { + printk(XENLOG_ERR LIVEPATCH "%s .altinstructions provided, but no .altinstr_replacement\n", + elf->name); + return -EINVAL; + } + start = sec->load_addr; end = sec->load_addr + sec->sec->sh_size; for ( a = start; a < end; a++ ) { - const void *instr = ALT_ORIG_PTR(a); - const void *replacement = ALT_REPL_PTR(a); + const void *orig = ALT_ORIG_PTR(a); + const void *repl = ALT_REPL_PTR(a); + + /* orig must be fully within .text. */ + if ( orig < payload->text_addr || + a->orig_len > payload->text_size || + orig + a->orig_len > payload->text_addr + payload->text_size ) + { + printk(XENLOG_ERR LIVEPATCH + "%s Alternative orig %p+%#x outside payload text %p+%#zx\n", + elf->name, orig, a->orig_len, + payload->text_addr, payload->text_size); + return -EINVAL; + } - if ( (instr < region->start && instr >= region->end) || - (replacement < region->start && replacement >= region->end) ) + /* + * repl must be fully within .altinstr_replacement, even if the + * replacement and the section happen to both have zero length. + */ + if ( repl < repl_sec->load_addr || + a->repl_len > repl_sec->sec->sh_size || + repl + a->repl_len > repl_sec->load_addr + repl_sec->sec->sh_size ) { - printk(XENLOG_ERR LIVEPATCH "%s Alt patching outside payload: %p\n", - elf->name, instr); + printk(XENLOG_ERR LIVEPATCH + "%s Alternative repl %p+%#x outside .altinstr_replacement %p+%#"PRIxElfWord"\n", + elf->name, repl, a->repl_len, + repl_sec->load_addr, repl_sec->sec->sh_size); return -EINVAL; } } apply_alternatives(start, end); + alt_done:; #else printk(XENLOG_ERR LIVEPATCH "%s: We don't support alternative patching\n", elf->name); diff --git a/xen/include/xen/elfstructs.h b/xen/include/xen/elfstructs.h index 3124469faeb4..eb6b87a823a8 100644 --- a/xen/include/xen/elfstructs.h +++ b/xen/include/xen/elfstructs.h @@ -563,6 +563,7 @@ typedef struct { #if defined(ELFSIZE) && (ELFSIZE == 32) #define PRIxElfAddr PRIx32 #define PRIuElfWord PRIu32 +#define PRIxElfWord PRIx32 #define Elf_Ehdr Elf32_Ehdr #define Elf_Phdr Elf32_Phdr @@ -591,6 +592,7 @@ typedef struct { #elif defined(ELFSIZE) && (ELFSIZE == 64) #define PRIxElfAddr PRIx64 #define PRIuElfWord PRIu64 +#define PRIxElfWord PRIx64 #define Elf_Ehdr Elf64_Ehdr #define Elf_Phdr Elf64_Phdr