From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from cmx-mtlrgo001.bell.net (mta-mtl-007.bell.net [209.71.208.29]) (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 E2F372F32 for ; Mon, 21 Jul 2025 19:16:30 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.71.208.29 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1753125393; cv=none; b=a0C6FJ2cysLTBW7TAWHXO1PdBUjnC8chTHzClerAGAXFHyxeoqN2nvUSMcZ4UkvugTUvN/dAZVHzfI97dY7TSjs9IAlSykUNZ6EK0cRMMc9eGwO/ncEYKGyiT740gb7PV6GKVweZyXQqL8RZNtuUcYAbvBSeiV4HVYyfhlfIllM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1753125393; c=relaxed/simple; bh=SndjvEtC0EbVUcPOZbn2mnV7oiYKyphhMGevsmTCOrc=; h=Date:From:To:Cc:Subject:Message-ID:MIME-Version:Content-Type: Content-Disposition; b=kL3fX1/Nw1vhVBsH/wzMQMDVbQXatFMD4KU6p1ivAjyrw3ttqI2sNGp3wtv5ukw86E3gMmR7FO0j5ANE0cOj6Sw4yY/udELcW7afPEQ2OXJqJK5BqQzgFanbimKRRb4dX0FTtvWMy5itVugI6IME11vkWdtyFL9mlY6o0rNWnZI= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=bell.net; spf=pass smtp.mailfrom=bell.net; dkim=pass (2048-bit key) header.d=bell.net header.i=@bell.net header.b=GqwPuQpB; arc=none smtp.client-ip=209.71.208.29 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=bell.net Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=bell.net Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=bell.net header.i=@bell.net header.b="GqwPuQpB" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=bell.net; s=selector1; t=1753125391; bh=5y1jAxIPjKBShkB1/hWzC9zdVSNdxye7NziF/jsOma4=; h=Date:From:To:Subject:Message-ID:MIME-Version:Content-Type; b=GqwPuQpBXWTxay0qGaS7fNtOy2g8+CszpZV6kyahYy9joxsRDTW2aBaFiUPOXF+KuKbOnekjAUux/O4JY+eTG9V38edjA59hBwKL0jncQ7QRPKQJswGDKV2ttJZYV0AFfFG/m5z7TzMCbLgITQOLf0ZzykOvTm9cEzVxtIrSmHq/ccVNb8C3Bkh6qIWhnfoX86V1mpe2PPM/qhMNUV/pulhi0FWaz8Z5+TVcrFmLiI5JPk7qNSaN2zVbg41WJF203xz0jNe1r9odcATVVZtkIzb+lc0Wj8WlnKCxesYtfV6V9LaWFU6XHaxO+69qBh1gluAlc05JSXZnOlvC9MZIeA== X-RG-SOPHOS: Clean X-RG-VADE-SC: 0 X-RG-VADE: Clean X-RG-Env-Sender: dave.anglin@bell.net X-RG-Rigid: 687D26C20030EA27 X-RazorGate-Vade: 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 X-RazorGate-Vade-Verdict: clean 0 X-RazorGate-Vade-Classification: clean Received: from mx3210.local (142.126.136.104) by cmx-mtlrgo001.bell.net (authenticated as dave.anglin@bell.net) id 687D26C20030EA27; Mon, 21 Jul 2025 15:13:44 -0400 Date: Mon, 21 Jul 2025 15:13:42 -0400 From: John David Anglin To: linux-parisc@vger.kernel.org Cc: Helge Deller , "James E.J. Bottomley" Subject: [PATCH] parisc: Update comments in make_insert_tlb Message-ID: Precedence: bulk X-Mailing-List: linux-parisc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="XtWV4BlMIQdUAgvB" Content-Disposition: inline --XtWV4BlMIQdUAgvB Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable parisc: Update comments in make_insert_tlb 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 =3D sysconf(_SC_PAGESIZE); char *p =3D 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 =3D (char *) ((((uintptr_t) p) + (2*page_size - 1)) & ~(page_si= ze - 1)); /* Drop PROT_READ protection. Kernel and userspace should fault when acce= ssing that memory region */ mprotect(p_aligned, page_size, PROT_NONE); /* the following write() should return EFAULT, since PROT_READ was droppe= d by previous mprotect() */ int ret =3D write(2, p_aligned, 1); if (!ret || errno !=3D 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 --- diff --git a/arch/parisc/kernel/entry.S b/arch/parisc/kernel/entry.S index ea57bcc21dc5..f4bf61a34701 100644 --- 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 =3D=3D _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 =3D=3D _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 =20 /* 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 <=3D PL1). Thus, the kernel + * exception fault handler doesn't trigger when reading pages + * that aren't user read accessible */ extrd,u,*=3D \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 */ --XtWV4BlMIQdUAgvB Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iQIzBAABCAAdFiEEnRzl+6e9+DTrEhyEXb/Nrl8ZTfEFAmh+kV4ACgkQXb/Nrl8Z TfF71A/+LGdeleIGhIrRh/nKgjx5BdEIML2Rm4NmpZErbm3a7QDgAam+YXQiys4Y +CZQ3X89rDa3XHS7rn50sQW8yMBiCJLmGfJhMTQs4EbkXEfU9yzIi8PsnkNouFhv tTO9s21N2yMdFwL8GJjPrRn3qjwbFWkMh9ducoyjWWNgz/E16voOLG6kzdV0sAKf CpotUl7j9tIWCTfTlHYVvtUstJHTkFWVPzeX2HHfVeCyc5al3VDuCMPeMg4ijDt+ MwQWN/nasjndqBR31cvCjVaXTATUs/WUiB9DNXEvX8UVsJfuSZ0AfeOLn5bNfAMC HcO3cGA7Me52FZxZS0Cx8MOgqRiKgAdQD6lZjh7ThqqBWQ7gaZqYDXhMhxcAEgUh tba+vsvjkt8Pz1/awr3bwXi5/B4Hq9HQhxc5Vfjcv3w0oTYJZBsvUIjBO8ALhp7l 9oi6DzGekmIwCWuErPmRIkEm65AdkAXfTwY/mSNxfHlHzkJz2CZRvmvMqn1aBeqK IRJXtYeZsNEVkWeLAYmJBpobKPphV4mVYaYHqpv93J2mrMIzyTQZ+X4ZbjM+pjiG /VzpmGOzDzSVquYi7nf+LI7CgfCLiXEJDDfFuNhmjDx1OF7QvJOz774gK7UH9OkZ lzliMOqSMR4k3N5ci/tgVlZf6ifZiovipRItR7qbxmw49vvt5lU= =8mhO -----END PGP SIGNATURE----- --XtWV4BlMIQdUAgvB--