linux-kernel - Re: PROBLEM: fanotify

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Date:   Tue, 24 Nov 2020 09:45:07 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Paweł Jasiak <pawel@...iak.xyz>
Cc:     Jan Kara <jack@...e.cz>, linux-kernel@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, x86@...nel.org,
        Thomas Gleixner <tglx@...utronix.de>,
        Brian Gerst <brgerst@...il.com>,
        Andy Lutomirski <luto@...nel.org>
Subject: Re: PROBLEM: fanotify_mark EFAULT on x86

On Mon, Nov 23, 2020 at 11:46:51PM +0100, Paweł Jasiak wrote:
> On 23/11/20, Jan Kara wrote:
> > OK, with a help of Boris Petkov I think I have a fix that looks correct
> > (attach). Can you please try whether it works for you? Thanks!
> 
> Unfortunately I am getting a linker error.
> 
> ld: arch/x86/entry/syscall_32.o:(.rodata+0x54c): undefined reference to `__ia32_sys_ia32_fanotify_mark'

Because CONFIG_COMPAT is not set in your .config.

Jan, look at 121b32a58a3a and especially this hunk

diff --git a/arch/x86/kernel/Makefile b/arch/x86/kernel/Makefile
index 9b294c13809a..b8f89f78b8cd 100644
--- a/arch/x86/kernel/Makefile
+++ b/arch/x86/kernel/Makefile
@@ -53,6 +53,8 @@ obj-y                 += setup.o x86_init.o i8259.o irqinit.o
 obj-$(CONFIG_JUMP_LABEL)       += jump_label.o
 obj-$(CONFIG_IRQ_WORK)  += irq_work.o
 obj-y                  += probe_roms.o
+obj-$(CONFIG_X86_32)   += sys_ia32.o
+obj-$(CONFIG_IA32_EMULATION)   += sys_ia32.o

how it enables the ia32 syscalls depending on those config items. Now,
you have

 #ifdef CONFIG_COMPAT
-COMPAT_SYSCALL_DEFINE6(fanotify_mark,
+SYSCALL_DEFINE6(ia32_fanotify_mark,

which is under CONFIG_COMPAT which is not set in Paweł's config.

config COMPAT
        def_bool y
        depends on IA32_EMULATION || X86_X32

but it depends on those two config items.

However, it looks to me like ia32_fanotify_mark's definition should be
simply under CONFIG_X86_32 because:

IA32_EMULATION is 32-bit emulation on 64-bit kernels
X86_X32 is for the x32 ABI

But I could be missing an angle...

HTH.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette