linux-kernel - [tip: x86/urgent] x86/entry: Fix entry/exit mismatch on failed fast 32-bit syscalls

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Date:   Sat, 06 Mar 2021 12:18:52 -0000
From:   "tip-bot2 for Andy Lutomirski" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     Andy Lutomirski <luto@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Borislav Petkov <bp@...e.de>, stable@...r.kernel.org,
        x86@...nel.org, linux-kernel@...r.kernel.org
Subject: [tip: x86/urgent] x86/entry: Fix entry/exit mismatch on failed fast
 32-bit syscalls

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

Commit-ID:     5d5675df792ff67e74a500c4c94db0f99e6a10ef
Gitweb:        https://git.kernel.org/tip/5d5675df792ff67e74a500c4c94db0f99e6a10ef
Author:        Andy Lutomirski <luto@...nel.org>
AuthorDate:    Thu, 04 Mar 2021 11:05:54 -08:00
Committer:     Borislav Petkov <bp@...e.de>
CommitterDate: Sat, 06 Mar 2021 13:10:06 +01:00

x86/entry: Fix entry/exit mismatch on failed fast 32-bit syscalls

On a 32-bit fast syscall that fails to read its arguments from user
memory, the kernel currently does syscall exit work but not
syscall entry work.  This confuses audit and ptrace.  For example:

    $ ./tools/testing/selftests/x86/syscall_arg_fault_32
    ...
    strace: pid 264258: entering, ptrace_syscall_info.op == 2
    ...

This is a minimal fix intended for ease of backporting.  A more
complete cleanup is coming.

Fixes: 0b085e68f407 ("x86/entry: Consolidate 32/64 bit syscall entry")
Signed-off-by: Andy Lutomirski <luto@...nel.org>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Signed-off-by: Borislav Petkov <bp@...e.de>
Cc: stable@...r.kernel.org
Link: https://lore.kernel.org/r/8c82296ddf803b91f8d1e5eac89e5803ba54ab0e.1614884673.git.luto@kernel.org
---
 arch/x86/entry/common.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/x86/entry/common.c b/arch/x86/entry/common.c
index a2433ae..4efd39a 100644
--- a/arch/x86/entry/common.c
+++ b/arch/x86/entry/common.c
@@ -128,7 +128,8 @@ static noinstr bool __do_fast_syscall_32(struct pt_regs *regs)
 		regs->ax = -EFAULT;
 
 		instrumentation_end();
-		syscall_exit_to_user_mode(regs);
+		local_irq_disable();
+		irqentry_exit_to_user_mode(regs);
 		return false;
 	}