From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from galois.linutronix.de (Galois.linutronix.de [193.142.43.55]) (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 1B92231618F; Wed, 17 Sep 2025 13:55:13 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=193.142.43.55 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1758117316; cv=none; b=AXhZJqWqoB1IHUGamW05OqbHTP1DFtEkrO3uNyGCxV81MrJ+FlPOcxBX5Ir56H2jUg00uLyolL8wZZML+iwC17V/EOX59Oqne/m5JCWwZsFXcCh5cpalHCTLcodtpQo6fa2yWGcUEiAodWUun+sQZbFsaOPGn1cSVI3Qd5M2YfU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1758117316; c=relaxed/simple; bh=1AGIHscYWBRNoy3EWBTKwv6GY+iVKr3IBEs5X3T5hv0=; h=From:To:Cc:Subject:In-Reply-To:References:Date:Message-ID: MIME-Version:Content-Type; b=rX6EsspUkmmkPMP3MoRFIqpv3HApgyAa24YroagRDPLDoY+MVduBK8CWOwTS/NKhL8q6ZEm38SRTtCeU3UZkC/C1r0eoiS185KUFW6vxhDoFg+2/FhncszgyQU0SxIsk73jRdeK6up/Az8GoCyKHe7yWmWgd6T8hkRXSW7kZPMY= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linutronix.de; spf=pass smtp.mailfrom=linutronix.de; dkim=pass (2048-bit key) header.d=linutronix.de header.i=@linutronix.de header.b=htgrVUpN; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b=rrkryvZt; arc=none smtp.client-ip=193.142.43.55 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linutronix.de Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linutronix.de Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="htgrVUpN"; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="rrkryvZt" From: Thomas Gleixner DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1758117312; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=v6wijLJ6yPSQGb++9TSkyHX8aU2wWOVN2uZhv4Iw/Sg=; b=htgrVUpNqPrUTT6sap0+RKqY8mN+zAHUnhbm4XiqKktMI6nALNkdAU+PveIoIqDoof0yds R4dyZ6gGiKCQ3a4Nc7BxZsrZbq5o/1dkdzJF89dWlE5bxo4FGU/DKQdxc5qDuSx6IWcGwM xZEpals5M7jmJahtYkM4UjQYIPTbzm5isG7uJSgBVtgWxjaRLMmk23+XcwGBF+MSQzvI6v 2xxzUsP6k3TCT4jllVI0Y9goiWTEesxDYvzKvvSHvkD6tWS4IEfh3tWH92htAE4rcDWsrG 2MkzKaMJXJwz1o/1Bq7TybNJcwhwXYa8hgnaznHEUEb/wPH+Ds+SHmBFP6B91A== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1758117312; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=v6wijLJ6yPSQGb++9TSkyHX8aU2wWOVN2uZhv4Iw/Sg=; b=rrkryvZtbzDTZhErhLp6hLKXjabdn0poRB3ciKeE+zajjGUOV6BUMtFyRPOGkyL5t1KOhm b17M+ZxIpGo64yBQ== To: "Russell King (Oracle)" Cc: LKML , Linus Torvalds , Peter Zijlstra , kernel test robot , linux-arm-kernel@lists.infradead.org, Nathan Chancellor , Christophe Leroy , Darren Hart , Davidlohr Bueso , =?utf-8?Q?Andr=C3=A9?= Almeida , x86@kernel.org, Alexander Viro , Christian Brauner , Jan Kara , linux-fsdevel@vger.kernel.org Subject: Re: [patch V2 1/6] ARM: uaccess: Implement missing __get_user_asm_dword() In-Reply-To: References: <875xdhaaun.ffs@tglx> Date: Wed, 17 Sep 2025 15:55:10 +0200 Message-ID: <87y0qd89q9.ffs@tglx> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable On Wed, Sep 17 2025 at 10:41, Russell King wrote: > On Wed, Sep 17, 2025 at 07:48:00AM +0200, Thomas Gleixner wrote: > > Putting together a simple test case, where the only change is making > __gu_val an unsigned long long: > > t.c: In function =E2=80=98get_ptr=E2=80=99: > t.c:40:15: warning: cast to pointer from integer of different size [-Wint= -to-pointer-cast] > 40 | (x) =3D (__typeof__(*(ptr)))__gu_val; = \ > | ^ > t.c:21:9: note: in expansion of macro =E2=80=98__get_user_err=E2=80=99 > 21 | __get_user_err((x), (ptr), __gu_err, TUSER()); = \ > | ^~~~~~~~~~~~~~ > t.c:102:16: note: in expansion of macro =E2=80=98__get_user=E2=80=99 > 102 | return __get_user(p, ptr); > | ^~~~~~~~~~ > > In order for the code you are modifying to be reachable, you need to > build with CONFIG_CPU_SPECTRE disabled. This is produced by: > > int get_ptr(void **ptr) > { > void *p; > > return __get_user(p, ptr); > } Duh, yes. I hate get_user() and I did not notice, because the allmodconfig build breaks early due to frame size checks, so I was too lazy to find that config knob and built only a couple of things and an artificial test case for u64. But it actually can be solved solvable by switching the casting to: (x) =3D *(__force __typeof__(*(ptr)) *) &__gu_val; Not pretty, but after upping the frame size limit it builds an allmodconfig kernel. The proper thing to use the corresponding sized values within the case $SIZE sections i.e.: size 1: { u8 __gu_val; __get_user_asm_byte(__gu_val, __gu_addr, err, __t); (x) =3D *(__force __typeof__(*(ptr)) *) &__gu_val; break; } ... See below. > Feel free to try to solve this, but I can assure you that you certainly > are not the first. Several people have already tried. Obviously not hard enough. :) Thanks, tglx --- Subject: ARM: uaccess: Implement missing __get_user_asm_dword() From: Thomas Gleixner Date: Fri, 12 Sep 2025 20:16:11 +0200 When CONFIG_CPU_SPECTRE=3Dn then get_user() is missing the 8 byte ASM varia= nt for no real good reason. This prevents using get_user(u64) in generic code. Implement it as a sequence of two 4-byte reads with LE/BE awareness and fixup the size switch case to make get_user(*ptr, **usrptr) work. Reported-by: kernel test robot Signed-off-by: Thomas Gleixner Cc: Russell King Cc: linux-arm-kernel@lists.infradead.org Closes: https://lore.kernel.org/oe-kbuild-all/202509120155.pFgwfeUD-lkp@int= el.com/ --- V2a: Solve the *ptr issue vs. unsigned long long - Russell V2: New patch to fix the 0-day fallout --- arch/arm/include/asm/uaccess.h | 50 ++++++++++++++++++++++++++++++++++++= ----- 1 file changed, 44 insertions(+), 6 deletions(-) --- a/arch/arm/include/asm/uaccess.h +++ b/arch/arm/include/asm/uaccess.h @@ -286,19 +286,41 @@ extern int __put_user_8(void *, unsigned #define __get_user_err(x, ptr, err, __t) \ do { \ unsigned long __gu_addr =3D (unsigned long)(ptr); \ - unsigned long __gu_val; \ unsigned int __ua_flags; \ __chk_user_ptr(ptr); \ might_fault(); \ __ua_flags =3D uaccess_save_and_enable(); \ switch (sizeof(*(ptr))) { \ - case 1: __get_user_asm_byte(__gu_val, __gu_addr, err, __t); break; \ - case 2: __get_user_asm_half(__gu_val, __gu_addr, err, __t); break; \ - case 4: __get_user_asm_word(__gu_val, __gu_addr, err, __t); break; \ - default: (__gu_val) =3D __get_user_bad(); \ + case 1: { \ + u8 __gu_val; \ + __get_user_asm_byte(__gu_val, __gu_addr, err, __t); \ + (x) =3D *(__force __typeof__(*(ptr)) *) &__gu_val; \ + break; \ + } \ + case 2: { \ + u16 __gu_val; \ + __get_user_asm_half(__gu_val, __gu_addr, err, __t); \ + (x) =3D *(__force __typeof__(*(ptr)) *) &__gu_val; \ + break; \ + } \ + case 4: { \ + u32 __gu_val; \ + __get_user_asm_word(__gu_val, __gu_addr, err, __t); \ + (x) =3D *(__force __typeof__(*(ptr)) *) &__gu_val; \ + break; \ + } \ + case 8: { \ + u64 __gu_val; \ + __get_user_asm_dword(__gu_val, __gu_addr, err, __t); \ + (x) =3D *(__force __typeof__(*(ptr)) *) &__gu_val; \ + break; \ + } \ + default: { \ + unsigned long __gu_val; \ + (__gu_val) =3D __get_user_bad(); \ + } \ } \ uaccess_restore(__ua_flags); \ - (x) =3D (__typeof__(*(ptr)))__gu_val; \ } while (0) #endif =20 @@ -353,6 +375,22 @@ do { \ #define __get_user_asm_word(x, addr, err, __t) \ __get_user_asm(x, addr, err, "ldr" __t) =20 +#ifdef __ARMEB__ +#define __WORD0_OFFS 4 +#define __WORD1_OFFS 0 +#else +#define __WORD0_OFFS 0 +#define __WORD1_OFFS 4 +#endif + +#define __get_user_asm_dword(x, addr, err, __t) \ + ({ \ + unsigned long __w0, __w1; \ + __get_user_asm(__w0, addr + __WORD0_OFFS, err, "ldr" __t); \ + __get_user_asm(__w1, addr + __WORD1_OFFS, err, "ldr" __t); \ + (x) =3D ((u64)__w1 << 32) | (u64) __w0; \ +}) + #define __put_user_switch(x, ptr, __err, __fn) \ do { \ const __typeof__(*(ptr)) __user *__pu_ptr =3D (ptr); \