netdev - Re: [PATCH] percpu: Remove intermediate variable in PERCPU

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Message-ID: <CAFULd4Z0PSzwvsFx_5deMKb7tV34uJWcHEadYGdk+D72QuHonA@mail.gmail.com>
Date: Thu, 19 Dec 2024 17:02:23 +0100
From: Uros Bizjak <ubizjak@...il.com>
To: Gal Pressman <gal@...dia.com>
Cc: Dennis Zhou <dennis@...nel.org>, Tejun Heo <tj@...nel.org>, Christoph Lameter <cl@...ux.com>, 
	Nathan Chancellor <nathan@...nel.org>, Nick Desaulniers <ndesaulniers@...gle.com>, 
	Bill Wendling <morbo@...gle.com>, Justin Stitt <justinstitt@...gle.com>, 
	Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org, 
	linux-kernel@...r.kernel.org, llvm@...ts.linux.dev, netdev@...r.kernel.org
Subject: Re: [PATCH] percpu: Remove intermediate variable in PERCPU_PTR()

On Thu, Dec 19, 2024 at 1:30 PM Uros Bizjak <ubizjak@...il.com> wrote:
>
> On Thu, Dec 19, 2024 at 1:18 PM Gal Pressman <gal@...dia.com> wrote:
> >
> > The intermediate variable in the PERCPU_PTR() macro results in a kernel
> > panic on boot [1] due to a compiler bug seen when compiling the kernel
> > (+ KASAN) with gcc 11.3.1, but not when compiling with latest gcc
> > (v14.2)/clang(v18.1).
> >
> > To solve it, remove the intermediate variable (which is not needed) and
> > keep the casting that resolves the address space checks.
> >
> > [1]
> >   Oops: general protection fault, probably for non-canonical address 0xdffffc0000000003: 0000 [#1] SMP KASAN
> >   KASAN: null-ptr-deref in range [0x0000000000000018-0x000000000000001f]
> >   CPU: 0 UID: 0 PID: 547 Comm: iptables Not tainted 6.13.0-rc1_external_tested-master #1
> >   Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.13.0-0-gf21b5a4aeb02-prebuilt.qemu.org 04/01/2014
> >   RIP: 0010:nf_ct_netns_do_get+0x139/0x540
> >   Code: 03 00 00 48 81 c4 88 00 00 00 5b 5d 41 5c 41 5d 41 5e 41 5f c3 4d 8d 75 08 48 b8 00 00 00 00 00 fc ff df 4c 89 f2 48 c1 ea 03 <0f> b6 04 02 84 c0 74 08 3c 03 0f 8e 27 03 00 00 41 8b 45 08 83 c0
> >   RSP: 0018:ffff888116df75e8 EFLAGS: 00010207
> >   RAX: dffffc0000000000 RBX: 1ffff11022dbeebe RCX: ffffffff839a2382
> >   RDX: 0000000000000003 RSI: 0000000000000008 RDI: ffff88842ec46d10
> >   RBP: 0000000000000002 R08: 0000000000000000 R09: fffffbfff0b0860c
> >   R10: ffff888116df75e8 R11: 0000000000000001 R12: ffffffff879d6a80
> >   R13: 0000000000000016 R14: 000000000000001e R15: ffff888116df7908
> >   FS:  00007fba01646740(0000) GS:ffff88842ec00000(0000) knlGS:0000000000000000
> >   CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> >   CR2: 000055bd901800d8 CR3: 00000001205f0003 CR4: 0000000000172eb0
> >   Call Trace:
> >    <TASK>
> >    ? die_addr+0x3d/0xa0
> >    ? exc_general_protection+0x144/0x220
> >    ? asm_exc_general_protection+0x22/0x30
> >    ? __mutex_lock+0x2c2/0x1d70
> >    ? nf_ct_netns_do_get+0x139/0x540
> >    ? nf_ct_netns_do_get+0xb5/0x540
> >    ? net_generic+0x1f0/0x1f0
> >    ? __create_object+0x5e/0x80
> >    xt_check_target+0x1f0/0x930
> >    ? textify_hooks.constprop.0+0x110/0x110
> >    ? pcpu_alloc_noprof+0x7cd/0xcf0
> >    ? xt_find_target+0x148/0x1e0
> >    find_check_entry.constprop.0+0x6c0/0x920
> >    ? get_info+0x380/0x380
> >    ? __virt_addr_valid+0x1df/0x3b0
> >    ? kasan_quarantine_put+0xe3/0x200
> >    ? kfree+0x13e/0x3d0
> >    ? translate_table+0xaf5/0x1750
> >    translate_table+0xbd8/0x1750
> >    ? ipt_unregister_table_exit+0x30/0x30
> >    ? __might_fault+0xbb/0x170
> >    do_ipt_set_ctl+0x408/0x1340
> >    ? nf_sockopt_find.constprop.0+0x17b/0x1f0
> >    ? lock_downgrade+0x680/0x680
> >    ? lockdep_hardirqs_on_prepare+0x284/0x400
> >    ? ipt_register_table+0x440/0x440
> >    ? bit_wait_timeout+0x160/0x160
> >    nf_setsockopt+0x6f/0xd0
> >    raw_setsockopt+0x7e/0x200
> >    ? raw_bind+0x590/0x590
> >    ? do_user_addr_fault+0x812/0xd20
> >    do_sock_setsockopt+0x1e2/0x3f0
> >    ? move_addr_to_user+0x90/0x90
> >    ? lock_downgrade+0x680/0x680
> >    __sys_setsockopt+0x9e/0x100
> >    __x64_sys_setsockopt+0xb9/0x150
> >    ? do_syscall_64+0x33/0x140
> >    do_syscall_64+0x6d/0x140
> >    entry_SYSCALL_64_after_hwframe+0x4b/0x53
> >   RIP: 0033:0x7fba015134ce
> >   Code: 0f 1f 40 00 48 8b 15 59 69 0e 00 f7 d8 64 89 02 48 c7 c0 ff ff ff ff eb b1 0f 1f 00 f3 0f 1e fa 49 89 ca b8 36 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 0a c3 66 0f 1f 84 00 00 00 00 00 48 8b 15 21
> >   RSP: 002b:00007ffd9de6f388 EFLAGS: 00000246 ORIG_RAX: 0000000000000036
> >   RAX: ffffffffffffffda RBX: 000055bd9017f490 RCX: 00007fba015134ce
> >   RDX: 0000000000000040 RSI: 0000000000000000 RDI: 0000000000000004
> >   RBP: 0000000000000500 R08: 0000000000000560 R09: 0000000000000052
> >   R10: 000055bd901800e0 R11: 0000000000000246 R12: 000055bd90180140
> >   R13: 000055bd901800e0 R14: 000055bd9017f498 R15: 000055bd9017ff10
> >    </TASK>
> >   Modules linked in: xt_MASQUERADE nf_conntrack_netlink nfnetlink xt_addrtype iptable_nat nf_nat br_netfilter rpcsec_gss_krb5 auth_rpcgss oid_registry overlay zram zsmalloc mlx4_ib mlx4_en mlx4_core rpcrdma rdma_ucm ib_uverbs ib_iser libiscsi scsi_transport_iscsi fuse ib_umad rdma_cm ib_ipoib iw_cm ib_cm ib_core
> >   ---[ end trace 0000000000000000 ]---
> >
> > Fixes: dabddd687c9e ("percpu: cast percpu pointer in PERCPU_PTR() via unsigned long")
> > Closes: https://lore.kernel.org/all/7590f546-4021-4602-9252-0d525de35b52@nvidia.com
> > Cc: Uros Bizjak <ubizjak@...il.com>
> > Signed-off-by: Gal Pressman <gal@...dia.com>
>
> Reviewed-by: Uros Bizjak <ubizjak@...il.com>
>
> > ---
> >  include/linux/percpu-defs.h | 3 +--
> >  1 file changed, 1 insertion(+), 2 deletions(-)
> >
> > diff --git a/include/linux/percpu-defs.h b/include/linux/percpu-defs.h
> > index 35842d1e3879..573adb643d90 100644
> > --- a/include/linux/percpu-defs.h
> > +++ b/include/linux/percpu-defs.h
> > @@ -222,8 +222,7 @@ do {                                                                        \
> >
> >  #define PERCPU_PTR(__p)                                                        \
> >  ({                                                                     \
> > -       unsigned long __pcpu_ptr = (__force unsigned long)(__p);        \
> > -       (typeof(*(__p)) __force __kernel *)(__pcpu_ptr);                \
> > +       (typeof(*(__p)) __force __kernel *)((__force unsigned long)(__p)); \
> >  })

Actually, you can simplify the above a bit by writing it as:

#define PERCPU_PTR(__p)                            \
    ((typeof(*(__p)) __force __kernel *)(__force unsigned long)(__p)) \

Uros.