linux-kernel - [tip: x86/shstk] x86/shstk: Check that SSP is aligned on sigreturn

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>] [day] [month] [year] [list]

Message-ID: <168694301494.404.16782501347946423933.tip-bot2@tip-bot2>
Date:   Fri, 16 Jun 2023 19:16:54 -0000
From:   "tip-bot2 for Rick Edgecombe" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     Rick Edgecombe <rick.p.edgecombe@...el.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: [tip: x86/shstk] x86/shstk: Check that SSP is aligned on sigreturn

The following commit has been merged into the x86/shstk branch of tip:

Commit-ID:     1d784497577b8f30374e4c0f12fbf1cb98986416
Gitweb:        https://git.kernel.org/tip/1d784497577b8f30374e4c0f12fbf1cb98986416
Author:        Rick Edgecombe <rick.p.edgecombe@...el.com>
AuthorDate:    Mon, 12 Jun 2023 17:10:58 -07:00
Committer:     Dave Hansen <dave.hansen@...ux.intel.com>
CommitterDate: Thu, 15 Jun 2023 16:31:34 -07:00

x86/shstk: Check that SSP is aligned on sigreturn

The shadow stack signal frame is read by the kernel on sigreturn. It
relies on shadow stack memory protections to prevent forgeries of this
signal frame (which included the pre-signal SSP). It also relies on the
shadow stack signal frame to have bit 63 set. Since this bit would not be
set via typical shadow stack operations, so the kernel can assume it was a
value it placed there.

However, in order to support 32 bit shadow stack, the INCSSPD instruction
can increment the shadow stack by 4 bytes. In this case SSP might be
pointing to a region spanning two 8 byte shadow stack frames. It could
confuse the checks described above.

Since the kernel only supports shadow stack in 64 bit, just check that
the SSP is 8 byte aligned in the sigreturn path.

Signed-off-by: Rick Edgecombe <rick.p.edgecombe@...el.com>
Signed-off-by: Dave Hansen <dave.hansen@...ux.intel.com>
Link: https://lore.kernel.org/all/20230613001108.3040476-33-rick.p.edgecombe%40intel.com
---
 arch/x86/kernel/shstk.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/arch/x86/kernel/shstk.c b/arch/x86/kernel/shstk.c
index f02e8ea..a8705f7 100644
--- a/arch/x86/kernel/shstk.c
+++ b/arch/x86/kernel/shstk.c
@@ -252,6 +252,9 @@ static int shstk_pop_sigframe(unsigned long *ssp)
 	unsigned long token_addr;
 	int err;

+	if (!IS_ALIGNED(*ssp, 8))
+		return -EINVAL;
+
 	err = get_shstk_data(&token_addr, (unsigned long __user *)*ssp);
 	if (unlikely(err))
 		return err;