From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 376A72BE643; Tue, 26 Aug 2025 11:40:02 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1756208403; cv=none; b=iTx5p5IijJSPQm1IscYcM74AZxkY5C983gLixbM9ZsJk+VQRiugLsWUTayw1CiBEgWoVioy1+RqCYpZDnZrt8h13EVp3DnyVeLGUzabMye/DI0uDG+J/zzGmX1QYORYXYb/LO8h3qLmlJmngaJHuwdmu8vmf+hKCK1AUod+0RxY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1756208403; c=relaxed/simple; bh=XFcLju0UdtT6JAullpycXv6+2bwGLIFq9NnaC7A+qwU=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=hV3/QwID7YW7BeVXti+Is3pA8SC6RsK/g5tpVcQLeTX9mEUONpJm3cspun9O2EvrR8U0DBwBItHDj5VI9bQXXS3RlFLwsMF7MNKwL3BfLOKcpPOj3zZh2E+aGcHRY6wYqkejDUcdjbFcKBrLyoinP1op5Ds4MglqjILfWFZh7h8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=U3ENPJuG; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="U3ENPJuG" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 65BB5C4CEF1; Tue, 26 Aug 2025 11:40:02 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1756208402; bh=XFcLju0UdtT6JAullpycXv6+2bwGLIFq9NnaC7A+qwU=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=U3ENPJuGQCGJ5jqiGzd+XNvN2d++CwlzTQqhWlBBrrXD4wRd6Gh24qJyUBt2lQU+Z nA36TAcNX7ODQ0c7ni40sJXdP5QYDipn0TPVPdufU9l5lrsENT3QV62OXvJ891WXgj 8tdPPZktDs2tCReoJVgYGo797RP8u+pYzrxJ6NpQ= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, John David Anglin , Helge Deller Subject: [PATCH 6.12 097/322] parisc: Update comments in make_insert_tlb Date: Tue, 26 Aug 2025 13:08:32 +0200 Message-ID: <20250826110918.083972972@linuxfoundation.org> X-Mailer: git-send-email 2.50.1 In-Reply-To: <20250826110915.169062587@linuxfoundation.org> References: <20250826110915.169062587@linuxfoundation.org> User-Agent: quilt/0.68 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.12-stable review patch. If anyone has any objections, please let me know. ------------------ From: John David Anglin commit cb22f247f371bd206a88cf0e0c05d80b8b62fb26 upstream. The following testcase exposed a problem with our read access checks in get_user() and raw_copy_from_user(): #include #include #include #include #include #include #include #include #include int main(int argc, char **argv) { unsigned long page_size = sysconf(_SC_PAGESIZE); char *p = malloc(3 * page_size); char *p_aligned; /* initialize memory region. If not initialized, write syscall below will correctly return EFAULT. */ if (1) memset(p, 'X', 3 * page_size); p_aligned = (char *) ((((uintptr_t) p) + (2*page_size - 1)) & ~(page_size - 1)); /* Drop PROT_READ protection. Kernel and userspace should fault when accessing that memory region */ mprotect(p_aligned, page_size, PROT_NONE); /* the following write() should return EFAULT, since PROT_READ was dropped by previous mprotect() */ int ret = write(2, p_aligned, 1); if (!ret || errno != EFAULT) printf("\n FAILURE: write() did not returned expected EFAULT value\n"); return 0; } Because of the way _PAGE_READ is handled, kernel code never generates a read access fault when it access a page as the kernel privilege level is always less than PL1 in the PTE. This patch reworks the comments in the make_insert_tlb macro to try to make this clearer. Signed-off-by: John David Anglin Signed-off-by: Helge Deller Cc: stable@vger.kernel.org # v5.12+ Signed-off-by: Greg Kroah-Hartman --- arch/parisc/kernel/entry.S | 17 ++++++++++++----- 1 file changed, 12 insertions(+), 5 deletions(-) --- a/arch/parisc/kernel/entry.S +++ b/arch/parisc/kernel/entry.S @@ -499,6 +499,12 @@ * this happens is quite subtle, read below */ .macro make_insert_tlb spc,pte,prot,tmp space_to_prot \spc \prot /* create prot id from space */ + +#if _PAGE_SPECIAL_BIT == _PAGE_DMB_BIT + /* need to drop DMB bit, as it's used as SPECIAL flag */ + depi 0,_PAGE_SPECIAL_BIT,1,\pte +#endif + /* The following is the real subtlety. This is depositing * T <-> _PAGE_REFTRAP * D <-> _PAGE_DIRTY @@ -511,17 +517,18 @@ * Finally, _PAGE_READ goes in the top bit of PL1 (so we * trigger an access rights trap in user space if the user * tries to read an unreadable page */ -#if _PAGE_SPECIAL_BIT == _PAGE_DMB_BIT - /* need to drop DMB bit, as it's used as SPECIAL flag */ - depi 0,_PAGE_SPECIAL_BIT,1,\pte -#endif depd \pte,8,7,\prot /* PAGE_USER indicates the page can be read with user privileges, * so deposit X1|11 to PL1|PL2 (remember the upper bit of PL1 - * contains _PAGE_READ) */ + * contains _PAGE_READ). While the kernel can't directly write + * user pages which have _PAGE_WRITE zero, it can read pages + * which have _PAGE_READ zero (PL <= PL1). Thus, the kernel + * exception fault handler doesn't trigger when reading pages + * that aren't user read accessible */ extrd,u,*= \pte,_PAGE_USER_BIT+32,1,%r0 depdi 7,11,3,\prot + /* If we're a gateway page, drop PL2 back to zero for promotion * to kernel privilege (so we can execute the page as kernel). * Any privilege promotion page always denys read and write */