linux-kernel - [PATCH v4 15/22] x86/fpu/xstate: Support ptracer-induced xstate buffer expansion

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <20210221185637.19281-16-chang.seok.bae@intel.com>
Date:   Sun, 21 Feb 2021 10:56:30 -0800
From:   "Chang S. Bae" <chang.seok.bae@...el.com>
To:     bp@...e.de, luto@...nel.org, tglx@...utronix.de, mingo@...nel.org,
        x86@...nel.org
Cc:     len.brown@...el.com, dave.hansen@...el.com, jing2.liu@...el.com,
        ravi.v.shankar@...el.com, linux-kernel@...r.kernel.org,
        chang.seok.bae@...el.com
Subject: [PATCH v4 15/22] x86/fpu/xstate: Support ptracer-induced xstate buffer expansion

ptrace() may update xstate data before the target task has taken an XFD
fault and expanded the xstate buffer. Detect this case and allocate a
sufficient buffer to support the request. Also, disable the (now
unnecessary) associated first-use fault.

Signed-off-by: Chang S. Bae <chang.seok.bae@...el.com>
Reviewed-by: Len Brown <len.brown@...el.com>
Cc: x86@...nel.org
Cc: linux-kernel@...r.kernel.org
---
Changes from v3:
* Removed 'no functional changes' in the changelog. (Borislav Petkov)

Changes from v2:
* Updated the changelog with task->fpu removed. (Borislav Petkov)
* Updated the code comments.
---
 arch/x86/kernel/fpu/regset.c | 29 +++++++++++++++++++++++++++++
 1 file changed, 29 insertions(+)

diff --git a/arch/x86/kernel/fpu/regset.c b/arch/x86/kernel/fpu/regset.c
index ee27df4caed6..ec6cbb75010e 100644
--- a/arch/x86/kernel/fpu/regset.c
+++ b/arch/x86/kernel/fpu/regset.c
@@ -122,6 +122,35 @@ int xstateregs_set(struct task_struct *target, const struct user_regset *regset,
 
 	xsave = &fpu->state->xsave;
 
+	/*
+	 * When a ptracer attempts to write any state in the target buffer but not
+	 * sufficiently allocated, it dynamically expands the buffer.
+	 */
+	if (count > get_xstate_size(fpu->state_mask)) {
+		unsigned int offset, size;
+		struct xstate_header hdr;
+		u64 mask;
+
+		offset = offsetof(struct xregs_state, header);
+		size = sizeof(hdr);
+
+		/* Retrieve XSTATE_BV */
+		if (kbuf) {
+			memcpy(&hdr, kbuf + offset, size);
+		} else {
+			ret = __copy_from_user(&hdr, ubuf + offset, size);
+			if (ret)
+				return ret;
+		}
+
+		mask = hdr.xfeatures & xfeatures_mask_user_dynamic;
+		if (!mask) {
+			ret = alloc_xstate_buffer(fpu, mask);
+			if (ret)
+				return ret;
+		}
+	}
+
 	fpu__prepare_write(fpu);
 
 	if (using_compacted_format()) {
-- 
2.17.1