linux-kernel - Re: [PATCH v14 1/4] asm-generic,arm64: create task variant of access

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Date:   Wed, 29 Mar 2023 19:13:22 +0200
From:   Oleg Nesterov <oleg@...hat.com>
To:     Gregory Price <gregory.price@...verge.com>
Cc:     Arnd Bergmann <arnd@...db.de>,
        Gregory Price <gourry.memverge@...il.com>,
        linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        Linux-Arch <linux-arch@...r.kernel.org>, avagin@...il.com,
        Peter Zijlstra <peterz@...radead.org>,
        Andy Lutomirski <luto@...nel.org>, krisman@...labora.com,
        Thomas Gleixner <tglx@...utronix.de>,
        Jonathan Corbet <corbet@....net>, shuah <shuah@...nel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Mark Rutland <mark.rutland@....com>, tongtiangen@...wei.com,
        Robin Murphy <robin.murphy@....com>
Subject: Re: [PATCH v14 1/4] asm-generic,arm64: create task variant of
 access_ok

On 03/28, Gregory Price wrote:
>
> Not sure how I should proceed here,

Can't we just kill this access_ok() in set_syscall_user_dispatch() ?
I don't think it buys too much.

Oleg.

diff --git a/kernel/entry/syscall_user_dispatch.c b/kernel/entry/syscall_user_dispatch.c
index 0b6379adff6b..d2e516ece52b 100644
--- a/kernel/entry/syscall_user_dispatch.c
+++ b/kernel/entry/syscall_user_dispatch.c
@@ -43,11 +43,7 @@ bool syscall_user_dispatch(struct pt_regs *regs)
 		return false;
 
 	if (likely(sd->selector)) {
-		/*
-		 * access_ok() is performed once, at prctl time, when
-		 * the selector is loaded by userspace.
-		 */
-		if (unlikely(__get_user(state, sd->selector))) {
+		if (unlikely(get_user(state, sd->selector))) {
 			force_exit_sig(SIGSEGV);
 			return true;
 		}
@@ -86,9 +82,6 @@ int set_syscall_user_dispatch(unsigned long mode, unsigned long offset,
 		if (offset && offset + len <= offset)
 			return -EINVAL;
 
-		if (selector && !access_ok(selector, sizeof(*selector)))
-			return -EFAULT;
-
 		break;
 	default:
 		return -EINVAL;