Re: [LKP] Re: [x86/mm/64] f154f29085: BUG:kernel_reboot-without-warning_in_boot_stage - clang KCOV?

Re: [LKP] Re: [x86/mm/64] f154f29085: BUG:kernel_reboot-without-warning_in_boot_stage - clang KCOV?

[Borislav Petkov]

Add Bruce and clang folks to the party.

On Thu, Dec 16, 2021 at 08:21:15PM +0800, Yin Fengwei wrote:
> Hi Boris,
> 
> On 12/16/2021 7:58 PM, Carel Si wrote:
> > Hi Boris,
> > 
> > On Thu, Dec 16, 2021 at 11:06:59AM +0100, Borislav Petkov wrote:
> >> On Thu, Dec 16, 2021 at 03:04:16PM +0800, Yin Fengwei wrote:
> >>> The testing was with Qemu.
> >>
> >> This is hardly what I asked for.
> >>
> >>> And we found that the hang is related with clang-14.
> >>
> >> I saw that already.
> >>
> >>> The original report showed the kernel is built with clang-14:
> >>>         # build kernel
> >>> 	cd linux
> >>> 	cp config-5.16.0-rc3-00003-gf154f290855b .config
> >>> 	make HOSTCC=clang-14 CC=clang-14 ARCH=x86_64 olddefconfig prepare modules_prepare bzImage modules
> >>> 	make HOSTCC=clang-14 CC=clang-14 ARCH=x86_64 INSTALL_MOD_PATH=<mod-install-dir> modules_install
> >>
> >> I saw that too.
> >>
> >>> Looks like KASAN related stub generated by clang-14 (KASAN_SHADOW_OFFSET and asan_report).
> >>> This function is early function called before kasan_init.
> >>>
> >>> Looks like we need to disable KASAN_SANITIZE for arch/x86/kernel/cpu/common.c. So clang-14 will
> >>> be happy with this kind of early TLB flush? Thanks.
> >>
> >> Ok, I don't understand: I asked for how exactly to reproduce and whether
> >> you can send me your vmlinux you built with your clang-14. What I get is
> >> some possible explanation about what might be happening.
> >>
> >> So what do you expect me to do? Say, "oh, sure, you're right, send me a
> >> patch" without even being able to see for myself what the root cause is?
> >>
> >> What if it is not the kernel's fault but clang-14 is miscompiling crap
> >> as in so many other cases?
> >>
> >> I built clang-14 and built with your .config and it works here fine. So
> >> why does yours fail?
> >>
> >> Or what's the point of all this?
> 
> I had concern that our report is an invalid report because you can't reproduce
> it in your side. If that's the case, it could waste more your time. That's why
> I did check and shared what I got. I am very sorry if I did it wrong.

Sure, you can always add your analysis but I'd like to reproduce myself
too. So, in the future, please answer the questions and then feel free
to add your analysis - I'll gladly have a look.

Which wasn't that far from the truth, btw.

But it isn't KASAN but GCOV profiling. Or is it KCOV profiling which
clang does.

That thing adds some counting glue to native_write_cr4():

(my comments from the actual singlestepping in qemu start with '##' below)

	movq	$__llvm_gcov_ctr.48+8, %rbx				##  mov    $0xffffffff8837d3c0,%rbx
.LBB8_1:                                # %set_register
                                        # =>This Inner Loop Header: Depth=1

	jmp	.Ltmp42
	...

.Ltmp42:                                # Block address taken
.LBB8_7:                                # %if.end79
        movq    %rbx, %rax						## 0xffffffff8837d3c0
        shrq    $3, %rax						## 0x1ffffffff106fa78
        movabsq $-2305847407260205056, %rcx     # imm = 0xDFFFFC0000000000	## 0xdffffc0000000000
        cmpb    $0, (%rax,%rcx)
        je      .LBB8_9

so the memory address CMP accesses is something as nonsensical as

  0xfffffbfff106fa78

so I'm guessing we need to setup something for that __llvm_gcov_ctr to
deref properly but I haven't dug deeper.

The important thing is that this triggers with clang-13 and -14. gcc is
fine with the same config but that probably is because gcc does other
profiling - gcov - I guess. Looking at the resulting asm, it has a bunch
of those counter increments:

        incq    __gcov0.native_write_cr4+88(%rip)       # __gcov0.native_write_cr4[11]

but no weird memory references.

So, clang folks, what's up?

The fix is simple but I'd like to understand first why does this fail
only with clang, 13 and newer.

(I mean, melver pointed me to

  380d53c45ff2 ("compiler_attributes.h: define __no_profile, add to noinstr")

which explains why 13 and newer).

Btw, joro, that second hunk is I think needed too because a couple of
lines earlier we set up the cr4 shadow so I think you should use it
instead of touching the hw CR4.

---
diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index 0083464de5e3..79b3d67addcc 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -384,7 +384,7 @@ void native_write_cr0(unsigned long val)
 }
 EXPORT_SYMBOL(native_write_cr0);
 
-void native_write_cr4(unsigned long val)
+void __no_profile native_write_cr4(unsigned long val)
 {
 	unsigned long bits_changed = 0;
 
diff --git a/arch/x86/kernel/head64.c b/arch/x86/kernel/head64.c
index 75acb6027a87..68d2b7f9a913 100644
--- a/arch/x86/kernel/head64.c
+++ b/arch/x86/kernel/head64.c
@@ -483,7 +483,7 @@ asmlinkage __visible void __init x86_64_start_kernel(char * real_mode_data)
 	/* Kill off the identity-map trampoline */
 	reset_early_page_tables();
 
-	__native_tlb_flush_global(native_read_cr4());
+	__native_tlb_flush_global(this_cpu_read(cpu_tlbstate.cr4));
 
 	clear_bss();
 


Leaving in the rest for the newly added folks.

> If you don't want to use lkp tool to reproduce the issue, following command
> could be used as well:
> 
> Use Qemu command so only kernel image need be downloaded:
> qemu-system-x86_64 -enable-kvm -cpu SandyBridge -smp 2 -m 16G -s -S -kernel vmlinuz-5.16.0-rc3-00003-gf154f290855b -nographic -append "console=ttyS0 earlyprintk=ttyS0,115200"
> to reproduce it.
> 
> 
> 
> Regards
> Yin, Fengwei
> 
> 
> 
> >>
> >> I mean, if you cannot send me what I ask for, you can say so. Then I can
> >> ignore this whole report altogether and waste my time somewhere else.
> > 
> > We have uploaded vmlinuz, modules.cgz, config as well as other related file to:
> > https://download.01.org/0day-ci/lkp-qemu/pkg/linux/x86_64-randconfig-a013-20211207/clang-14/f154f290855b070cc94dd44ad253c0ef8a9337bb/
> > 
> > Machine types can refer to:
> > https://zerobin.net/?e107cf7b56495d80#MQLh14wUT9Osv1tWCwiQx/okkAN48Nq+drVPE0PiNPw=
> > 
> > If there's any other msg needed, pls feel free to propose, thanks.
> > 
> > Below are our full steps to reproduce the issue:
> > 
> > # download lkp-tests
> > $ git clone https://github.com/intel/lkp-tests.git
> > 
> > $ cd lkp-tests/
> > 
> > # download vmlinuz
> > $ wget https://download.01.org/0day-ci/lkp-qemu/pkg/linux/x86_64-randconfig-a013-20211207/clang-14/f154f290855b070cc94dd44ad253c0ef8a9337bb/vmlinuz-5.16.0-rc3-00003-gf154f290855b
> > 
> > # dowmload modules.cgz
> > $ wget https://download.01.org/0day-ci/lkp-qemu/pkg/linux/x86_64-randconfig-a013-20211207/clang-14/f154f290855b070cc94dd44ad253c0ef8a9337bb/modules.cgz
> > 
> > # download job-script which is attached
> > 
> > # run lkp qemu
> > lkp-tests$ sudo bin/lkp qemu -k vmlinuz-5.16.0-rc3-00003-gf154f290855b -m modules.cgz job-script
> > 
> > ~/lkp-tests/pkg/lkp-src ~/lkp-tests
> > x86_64
> > ==> Making package: lkp-src 0-1 (Thu 16 Dec 2021 07:26:22 PM CST)
> > ==> Checking runtime dependencies...
> > ==> Checking buildtime dependencies...
> > ==> WARNING: Using existing $srcdir/ tree
> > ==> Removing existing $pkgdir/ directory...
> > ==> Starting build()...
> > make: Entering directory '/home/carel/lkp-tests/bin/event'
> > klcc  -D_FORTIFY_SOURCE=2  -c -o wakeup.o wakeup.c
> > klcc  -Wl,-O1,--sort-common,--as-needed,-z,relro -static -o wakeup wakeup.o
> > rm -f wakeup.o
> > strip wakeup
> > make: Leaving directory '/home/carel/lkp-tests/bin/event'
> > ==> Entering fakeroot environment...
> > x86_64
> > ==> Starting package()...
> > ==> Creating package "lkp-src"...
> > 103987 blocks
> > renamed '/home/carel/.lkp/cache/lkp-x86_64.cgz.tmp' -> '/home/carel/.lkp/cache/lkp-x86_64.cgz'
> > ==> Leaving fakeroot environment.
> > ==> Finished making: lkp-src 0-1 (Thu 16 Dec 2021 07:26:24 PM CST)
> > ~/lkp-tests
> > 12 blocks
> > result_root: /home/carel/.lkp//result/boot/1/vm-snb/debian-10.4-x86_64-20200603.cgz/x86_64-randconfig-a013-20211207/clang-14/f154f290855b070cc94dd44ad253c0ef8a9337bb/0
> > downloading initrds ...
> > use local modules: /home/carel/.lkp/cache/modules.cgz
> > /usr/bin/wget -q --timeout=1800 --tries=1 --local-encoding=UTF-8 http://0day.sh.intel.com:80/~lkp/osimage/debian/debian-10.4-x86_64-20200603.cgz -N -P /home/carel/.lkp/cache/osimage/debian
> > 440459 blocks
> > /usr/bin/wget -q --timeout=1800 --tries=1 --local-encoding=UTF-8 http://0day.sh.intel.com:80/~lkp/osimage/deps/debian-10.4-x86_64-20200603.cgz/run-ipconfig_20200608.cgz -N -P /home/carel/.lkp/cache/osimage/deps/debian-10.4-x86_64-20200603.cgz
> > 1773 blocks
> > /usr/bin/wget -q --timeout=1800 --tries=1 --local-encoding=UTF-8 http://0day.sh.intel.com:80/~lkp/osimage/deps/debian-10.4-x86_64-20200603.cgz/lkp_20210707.cgz -N -P /home/carel/.lkp/cache/osimage/deps/debian-10.4-x86_64-20200603.cgz
> > 2321 blocks
> > /usr/bin/wget -q --timeout=1800 --tries=1 --local-encoding=UTF-8 http://0day.sh.intel.com:80/~lkp/osimage/deps/debian-10.4-x86_64-20200603.cgz/rsync-rootfs_20200608.cgz -N -P /home/carel/.lkp/cache/osimage/deps/debian-10.4-x86_64-20200603.cgz
> > 6856 blocks
> > exec command: qemu-system-x86_64 -enable-kvm -fsdev local,id=test_dev,path=/home/carel/.lkp//result/boot/1/vm-snb/debian-10.4-x86_64-20200603.cgz/x86_64-randconfig-a013-20211207/clang-14/f154f290855b070cc94dd44ad253c0ef8a9337bb/0,security_model=none -device virtio-9p-pci,fsdev=test_dev,mount_tag=9p/virtfs_mount -kernel vmlinuz-5.16.0-rc3-00003-gf154f290855b -append root=/dev/ram0 user=lkp job=/lkp/jobs/scheduled/vm-snb-192/boot-1-debian-10.4-x86_64-20200603.cgz-f154f290855b070cc94dd44ad253c0ef8a9337bb-20211208-23538-lnvkeg-5.yaml ARCH=x86_64 kconfig=x86_64-randconfig-a013-20211207 branch=tip/x86/mm commit=f154f290855b070cc94dd44ad253c0ef8a9337bb BOOT_IMAGE=/pkg/linux/x86_64-randconfig-a013-20211207/clang-14/f154f290855b070cc94dd44ad253c0ef8a9337bb/vmlinuz-5.16.0-rc3-00003-gf154f290855b vmalloc=128M initramfs_async=0 page_owner=on max_uptime=600 RESULT_ROOT=/result/boot/1/vm-snb/debian-10.4-x86_64-20200603.cgz/x86_64-randconfig-a013-20211207/clang-14/f154f290855b070cc94dd44ad253c0ef8a9337bb/3 LKP_LOCAL_RUN=1 selinux=0 debug apic=debug sysrq_always_enabled rcupdate.rcu_cpu_stall_timeout=100 net.ifnames=0 printk.devkmsg=on panic=-1 softlockup_panic=1 nmi_watchdog=panic oops=panic load_ramdisk=2 prompt_ramdisk=0 drbd.minor_count=8 systemd.log_level=err ignore_loglevel console=tty0 earlyprintk=ttyS0,115200 console=ttyS0,115200 vga=normal rw  ip=dhcp result_service=9p/virtfs_mount -initrd /home/carel/.lkp/cache/final_initrd -smp 2 -m 3144M -no-reboot -watchdog i6300esb -rtc base=localtime -device e1000,netdev=net0 -netdev user,id=net0 -display none -monitor null -serial stdio
> > early console in setup code
> > early console in extract_kernel
> > input_data: 0x0000000006ffc2e0
> > input_len: 0x000000000260cb2b
> > output: 0x0000000001000000
> > output_len: 0x00000000079e7da4
> > kernel_total_size: 0x0000000008a2c000
> > needed_size: 0x0000000008c00000
> > trampoline_32bit: 0x000000000009d000
> > Physical KASLR using RDTSC...
> > Virtual KASLR using RDTSC...
> > 
> > Decompressing Linux... Parsing ELF... Performing relocations... done.
> > Booting the kernel.
> > 
> >>
> >> -- 
> >> Regards/Gruss,
> >>     Boris.
> >>
> >> SUSE Software Solutions Germany GmbH, GF: Ivo Totev, HRB 36809, AG Nürnberg

-- 
Regards/Gruss,
    Boris.

SUSE Software Solutions Germany GmbH, GF: Ivo Totev, HRB 36809, AG Nürnberg

Re: [LKP] Re: [x86/mm/64] f154f29085: BUG:kernel_reboot-without-warning_in_boot_stage - clang KCOV?

[Nathan Chancellor]

Hi Boris,

On Fri, Dec 17, 2021 at 01:52:53PM +0100, Borislav Petkov wrote:
> Add Bruce and clang folks to the party.
> 
> On Thu, Dec 16, 2021 at 08:21:15PM +0800, Yin Fengwei wrote:
> > Hi Boris,
> > 
> > On 12/16/2021 7:58 PM, Carel Si wrote:
> > > Hi Boris,
> > > 
> > > On Thu, Dec 16, 2021 at 11:06:59AM +0100, Borislav Petkov wrote:
> > >> On Thu, Dec 16, 2021 at 03:04:16PM +0800, Yin Fengwei wrote:
> > >>> The testing was with Qemu.
> > >>
> > >> This is hardly what I asked for.
> > >>
> > >>> And we found that the hang is related with clang-14.
> > >>
> > >> I saw that already.
> > >>
> > >>> The original report showed the kernel is built with clang-14:
> > >>>         # build kernel
> > >>> 	cd linux
> > >>> 	cp config-5.16.0-rc3-00003-gf154f290855b .config
> > >>> 	make HOSTCC=clang-14 CC=clang-14 ARCH=x86_64 olddefconfig prepare modules_prepare bzImage modules
> > >>> 	make HOSTCC=clang-14 CC=clang-14 ARCH=x86_64 INSTALL_MOD_PATH=<mod-install-dir> modules_install
> > >>
> > >> I saw that too.
> > >>
> > >>> Looks like KASAN related stub generated by clang-14 (KASAN_SHADOW_OFFSET and asan_report).
> > >>> This function is early function called before kasan_init.
> > >>>
> > >>> Looks like we need to disable KASAN_SANITIZE for arch/x86/kernel/cpu/common.c. So clang-14 will
> > >>> be happy with this kind of early TLB flush? Thanks.
> > >>
> > >> Ok, I don't understand: I asked for how exactly to reproduce and whether
> > >> you can send me your vmlinux you built with your clang-14. What I get is
> > >> some possible explanation about what might be happening.
> > >>
> > >> So what do you expect me to do? Say, "oh, sure, you're right, send me a
> > >> patch" without even being able to see for myself what the root cause is?
> > >>
> > >> What if it is not the kernel's fault but clang-14 is miscompiling crap
> > >> as in so many other cases?
> > >>
> > >> I built clang-14 and built with your .config and it works here fine. So
> > >> why does yours fail?
> > >>
> > >> Or what's the point of all this?
> > 
> > I had concern that our report is an invalid report because you can't reproduce
> > it in your side. If that's the case, it could waste more your time. That's why
> > I did check and shared what I got. I am very sorry if I did it wrong.
> 
> Sure, you can always add your analysis but I'd like to reproduce myself
> too. So, in the future, please answer the questions and then feel free
> to add your analysis - I'll gladly have a look.
> 
> Which wasn't that far from the truth, btw.
> 
> But it isn't KASAN but GCOV profiling. Or is it KCOV profiling which
> clang does.

This is GCOV, -fprofile-arcs.

> That thing adds some counting glue to native_write_cr4():
> 
> (my comments from the actual singlestepping in qemu start with '##' below)
> 
> 	movq	$__llvm_gcov_ctr.48+8, %rbx				##  mov    $0xffffffff8837d3c0,%rbx
> .LBB8_1:                                # %set_register
>                                         # =>This Inner Loop Header: Depth=1
> 
> 	jmp	.Ltmp42
> 	...
> 
> .Ltmp42:                                # Block address taken
> .LBB8_7:                                # %if.end79
>         movq    %rbx, %rax						## 0xffffffff8837d3c0
>         shrq    $3, %rax						## 0x1ffffffff106fa78
>         movabsq $-2305847407260205056, %rcx     # imm = 0xDFFFFC0000000000	## 0xdffffc0000000000
>         cmpb    $0, (%rax,%rcx)
>         je      .LBB8_9
> 
> so the memory address CMP accesses is something as nonsensical as
> 
>   0xfffffbfff106fa78
> 
> so I'm guessing we need to setup something for that __llvm_gcov_ctr to
> deref properly but I haven't dug deeper.

I am not reallys ure how exactly GCOV works under the hood so I cannot
really comment on it (Nick might); it seems like llvm_gcov_init needs to
get called for __llvm_gcov_ctr to get set up properly and maybe that
hasn't happened at the point.

> The important thing is that this triggers with clang-13 and -14. gcc is
> fine with the same config but that probably is because gcc does other
> profiling - gcov - I guess. Looking at the resulting asm, it has a bunch
> of those counter increments:
> 
>         incq    __gcov0.native_write_cr4+88(%rip)       # __gcov0.native_write_cr4[11]
> 
> but no weird memory references.
> 
> So, clang folks, what's up?
> 
> The fix is simple but I'd like to understand first why does this fail
> only with clang, 13 and newer.
> 
> (I mean, melver pointed me to
> 
>   380d53c45ff2 ("compiler_attributes.h: define __no_profile, add to noinstr")
> 
> which explains why 13 and newer).

This is a bit of a brain dump, apologies for not offering much upfront
analysis, I am not as familiar with LLVM internals as Nick but this
might help others look into the problem.

I ended up seeing this thread yesterday through a lore filter that I
have and I bisected LLVM based on the fact that it happened with
clang-13 but not clang-12; that bisect pointed out Nick's commit in LLVM
that added the no profile attribute, which means that GCOV and KASAN
need to be enabled to see this bug. I was not able to reproduce it with
just one of them enabled at a time.

With that, I removed the no profile attribute dependency on GCOV_KERNEL
and bisected again, landing on the commit in LLVM 13 that enables the
new pass manager, which fundamentally changes how LLVM transforms its
IR. Whenever that has happened in the past, it usually points to a
pre-existing issue; if I go back to clang-11 (the current minimum of
-next) and enable the NPM there with -fexperimental-new-pass-manager, I
see this hang so it seems like there might be some issue how GCOV and
KASAN are manipulated together in the context of the NPM that was not
present with the legacy pass manager. I do see tests in LLVM that test
to make sure __llvm_gcov_ctr does not get instrumented with KASAN, maybe
there is another interaction that should not be happening between those
two?

> Btw, joro, that second hunk is I think needed too because a couple of
> lines earlier we set up the cr4 shadow so I think you should use it
> instead of touching the hw CR4.
> 
> ---
> diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
> index 0083464de5e3..79b3d67addcc 100644
> --- a/arch/x86/kernel/cpu/common.c
> +++ b/arch/x86/kernel/cpu/common.c
> @@ -384,7 +384,7 @@ void native_write_cr0(unsigned long val)
>  }
>  EXPORT_SYMBOL(native_write_cr0);
>  
> -void native_write_cr4(unsigned long val)
> +void __no_profile native_write_cr4(unsigned long val)
>  {
>  	unsigned long bits_changed = 0;
>  
> diff --git a/arch/x86/kernel/head64.c b/arch/x86/kernel/head64.c
> index 75acb6027a87..68d2b7f9a913 100644
> --- a/arch/x86/kernel/head64.c
> +++ b/arch/x86/kernel/head64.c
> @@ -483,7 +483,7 @@ asmlinkage __visible void __init x86_64_start_kernel(char * real_mode_data)
>  	/* Kill off the identity-map trampoline */
>  	reset_early_page_tables();
>  
> -	__native_tlb_flush_global(native_read_cr4());
> +	__native_tlb_flush_global(this_cpu_read(cpu_tlbstate.cr4));
>  
>  	clear_bss();
>  
> 
> 
> Leaving in the rest for the newly added folks.
> 
> > If you don't want to use lkp tool to reproduce the issue, following command
> > could be used as well:
> > 
> > Use Qemu command so only kernel image need be downloaded:
> > qemu-system-x86_64 -enable-kvm -cpu SandyBridge -smp 2 -m 16G -s -S -kernel vmlinuz-5.16.0-rc3-00003-gf154f290855b -nographic -append "console=ttyS0 earlyprintk=ttyS0,115200"
> > to reproduce it.
> > 
> > 
> > 
> > Regards
> > Yin, Fengwei
> > 
> > 
> > 
> > >>
> > >> I mean, if you cannot send me what I ask for, you can say so. Then I can
> > >> ignore this whole report altogether and waste my time somewhere else.
> > > 
> > > We have uploaded vmlinuz, modules.cgz, config as well as other related file to:
> > > https://download.01.org/0day-ci/lkp-qemu/pkg/linux/x86_64-randconfig-a013-20211207/clang-14/f154f290855b070cc94dd44ad253c0ef8a9337bb/
> > > 
> > > Machine types can refer to:
> > > https://zerobin.net/?e107cf7b56495d80#MQLh14wUT9Osv1tWCwiQx/okkAN48Nq+drVPE0PiNPw=
> > > 
> > > If there's any other msg needed, pls feel free to propose, thanks.
> > > 
> > > Below are our full steps to reproduce the issue:
> > > 
> > > # download lkp-tests
> > > $ git clone https://github.com/intel/lkp-tests.git
> > > 
> > > $ cd lkp-tests/
> > > 
> > > # download vmlinuz
> > > $ wget https://download.01.org/0day-ci/lkp-qemu/pkg/linux/x86_64-randconfig-a013-20211207/clang-14/f154f290855b070cc94dd44ad253c0ef8a9337bb/vmlinuz-5.16.0-rc3-00003-gf154f290855b
> > > 
> > > # dowmload modules.cgz
> > > $ wget https://download.01.org/0day-ci/lkp-qemu/pkg/linux/x86_64-randconfig-a013-20211207/clang-14/f154f290855b070cc94dd44ad253c0ef8a9337bb/modules.cgz
> > > 
> > > # download job-script which is attached
> > > 
> > > # run lkp qemu
> > > lkp-tests$ sudo bin/lkp qemu -k vmlinuz-5.16.0-rc3-00003-gf154f290855b -m modules.cgz job-script
> > > 
> > > ~/lkp-tests/pkg/lkp-src ~/lkp-tests
> > > x86_64
> > > ==> Making package: lkp-src 0-1 (Thu 16 Dec 2021 07:26:22 PM CST)
> > > ==> Checking runtime dependencies...
> > > ==> Checking buildtime dependencies...
> > > ==> WARNING: Using existing $srcdir/ tree
> > > ==> Removing existing $pkgdir/ directory...
> > > ==> Starting build()...
> > > make: Entering directory '/home/carel/lkp-tests/bin/event'
> > > klcc  -D_FORTIFY_SOURCE=2  -c -o wakeup.o wakeup.c
> > > klcc  -Wl,-O1,--sort-common,--as-needed,-z,relro -static -o wakeup wakeup.o
> > > rm -f wakeup.o
> > > strip wakeup
> > > make: Leaving directory '/home/carel/lkp-tests/bin/event'
> > > ==> Entering fakeroot environment...
> > > x86_64
> > > ==> Starting package()...
> > > ==> Creating package "lkp-src"...
> > > 103987 blocks
> > > renamed '/home/carel/.lkp/cache/lkp-x86_64.cgz.tmp' -> '/home/carel/.lkp/cache/lkp-x86_64.cgz'
> > > ==> Leaving fakeroot environment.
> > > ==> Finished making: lkp-src 0-1 (Thu 16 Dec 2021 07:26:24 PM CST)
> > > ~/lkp-tests
> > > 12 blocks
> > > result_root: /home/carel/.lkp//result/boot/1/vm-snb/debian-10.4-x86_64-20200603.cgz/x86_64-randconfig-a013-20211207/clang-14/f154f290855b070cc94dd44ad253c0ef8a9337bb/0
> > > downloading initrds ...
> > > use local modules: /home/carel/.lkp/cache/modules.cgz
> > > /usr/bin/wget -q --timeout=1800 --tries=1 --local-encoding=UTF-8 http://0day.sh.intel.com:80/~lkp/osimage/debian/debian-10.4-x86_64-20200603.cgz -N -P /home/carel/.lkp/cache/osimage/debian
> > > 440459 blocks
> > > /usr/bin/wget -q --timeout=1800 --tries=1 --local-encoding=UTF-8 http://0day.sh.intel.com:80/~lkp/osimage/deps/debian-10.4-x86_64-20200603.cgz/run-ipconfig_20200608.cgz -N -P /home/carel/.lkp/cache/osimage/deps/debian-10.4-x86_64-20200603.cgz
> > > 1773 blocks
> > > /usr/bin/wget -q --timeout=1800 --tries=1 --local-encoding=UTF-8 http://0day.sh.intel.com:80/~lkp/osimage/deps/debian-10.4-x86_64-20200603.cgz/lkp_20210707.cgz -N -P /home/carel/.lkp/cache/osimage/deps/debian-10.4-x86_64-20200603.cgz
> > > 2321 blocks
> > > /usr/bin/wget -q --timeout=1800 --tries=1 --local-encoding=UTF-8 http://0day.sh.intel.com:80/~lkp/osimage/deps/debian-10.4-x86_64-20200603.cgz/rsync-rootfs_20200608.cgz -N -P /home/carel/.lkp/cache/osimage/deps/debian-10.4-x86_64-20200603.cgz
> > > 6856 blocks
> > > exec command: qemu-system-x86_64 -enable-kvm -fsdev local,id=test_dev,path=/home/carel/.lkp//result/boot/1/vm-snb/debian-10.4-x86_64-20200603.cgz/x86_64-randconfig-a013-20211207/clang-14/f154f290855b070cc94dd44ad253c0ef8a9337bb/0,security_model=none -device virtio-9p-pci,fsdev=test_dev,mount_tag=9p/virtfs_mount -kernel vmlinuz-5.16.0-rc3-00003-gf154f290855b -append root=/dev/ram0 user=lkp job=/lkp/jobs/scheduled/vm-snb-192/boot-1-debian-10.4-x86_64-20200603.cgz-f154f290855b070cc94dd44ad253c0ef8a9337bb-20211208-23538-lnvkeg-5.yaml ARCH=x86_64 kconfig=x86_64-randconfig-a013-20211207 branch=tip/x86/mm commit=f154f290855b070cc94dd44ad253c0ef8a9337bb BOOT_IMAGE=/pkg/linux/x86_64-randconfig-a013-20211207/clang-14/f154f290855b070cc94dd44ad253c0ef8a9337bb/vmlinuz-5.16.0-rc3-00003-gf154f290855b vmalloc=128M initramfs_async=0 page_owner=on max_uptime=600 RESULT_ROOT=/result/boot/1/vm-snb/debian-10.4-x86_64-20200603.cgz/x86_64-randconfig-a013-20211207/clang-14/f154f290855b070cc94dd44ad253c0ef8a9337bb/3 LKP_LOCAL_RUN=1 selinux=0 debug apic=debug sysrq_always_enabled rcupdate.rcu_cpu_stall_timeout=100 net.ifnames=0 printk.devkmsg=on panic=-1 softlockup_panic=1 nmi_watchdog=panic oops=panic load_ramdisk=2 prompt_ramdisk=0 drbd.minor_count=8 systemd.log_level=err ignore_loglevel console=tty0 earlyprintk=ttyS0,115200 console=ttyS0,115200 vga=normal rw  ip=dhcp result_service=9p/virtfs_mount -initrd /home/carel/.lkp/cache/final_initrd -smp 2 -m 3144M -no-reboot -watchdog i6300esb -rtc base=localtime -device e1000,netdev=net0 -netdev user,id=net0 -display none -monitor null -serial stdio
> > > early console in setup code
> > > early console in extract_kernel
> > > input_data: 0x0000000006ffc2e0
> > > input_len: 0x000000000260cb2b
> > > output: 0x0000000001000000
> > > output_len: 0x00000000079e7da4
> > > kernel_total_size: 0x0000000008a2c000
> > > needed_size: 0x0000000008c00000
> > > trampoline_32bit: 0x000000000009d000
> > > Physical KASLR using RDTSC...
> > > Virtual KASLR using RDTSC...
> > > 
> > > Decompressing Linux... Parsing ELF... Performing relocations... done.
> > > Booting the kernel.

Cheers,
Nathan

Re: [LKP] Re: [x86/mm/64] f154f29085: BUG:kernel_reboot-without-warning_in_boot_stage - clang KCOV?

[Yin Fengwei]

Hi Boris,

On 12/17/2021 8:52 PM, Borislav Petkov wrote:
> Add Bruce and clang folks to the party.
> 
> On Thu, Dec 16, 2021 at 08:21:15PM +0800, Yin Fengwei wrote:
>> Hi Boris,
>>
>> On 12/16/2021 7:58 PM, Carel Si wrote:
>>> Hi Boris,
>>>
>>> On Thu, Dec 16, 2021 at 11:06:59AM +0100, Borislav Petkov wrote:
>>>> On Thu, Dec 16, 2021 at 03:04:16PM +0800, Yin Fengwei wrote:
>>>>> The testing was with Qemu.
>>>>
>>>> This is hardly what I asked for.
>>>>
>>>>> And we found that the hang is related with clang-14.
>>>>
>>>> I saw that already.
>>>>
>>>>> The original report showed the kernel is built with clang-14:
>>>>>         # build kernel
>>>>> 	cd linux
>>>>> 	cp config-5.16.0-rc3-00003-gf154f290855b .config
>>>>> 	make HOSTCC=clang-14 CC=clang-14 ARCH=x86_64 olddefconfig prepare modules_prepare bzImage modules
>>>>> 	make HOSTCC=clang-14 CC=clang-14 ARCH=x86_64 INSTALL_MOD_PATH=<mod-install-dir> modules_install
>>>>
>>>> I saw that too.
>>>>
>>>>> Looks like KASAN related stub generated by clang-14 (KASAN_SHADOW_OFFSET and asan_report).
>>>>> This function is early function called before kasan_init.
>>>>>
>>>>> Looks like we need to disable KASAN_SANITIZE for arch/x86/kernel/cpu/common.c. So clang-14 will
>>>>> be happy with this kind of early TLB flush? Thanks.
>>>>
>>>> Ok, I don't understand: I asked for how exactly to reproduce and whether
>>>> you can send me your vmlinux you built with your clang-14. What I get is
>>>> some possible explanation about what might be happening.
>>>>
>>>> So what do you expect me to do? Say, "oh, sure, you're right, send me a
>>>> patch" without even being able to see for myself what the root cause is?
>>>>
>>>> What if it is not the kernel's fault but clang-14 is miscompiling crap
>>>> as in so many other cases?
>>>>
>>>> I built clang-14 and built with your .config and it works here fine. So
>>>> why does yours fail?
>>>>
>>>> Or what's the point of all this?
>>
>> I had concern that our report is an invalid report because you can't reproduce
>> it in your side. If that's the case, it could waste more your time. That's why
>> I did check and shared what I got. I am very sorry if I did it wrong.
> 
> Sure, you can always add your analysis but I'd like to reproduce myself
> too. So, in the future, please answer the questions and then feel free
> to add your analysis - I'll gladly have a look.
Thanks a lot for sharing this. Lessons learnt here. Will follow this
rule exactly in the future.

> 
> Which wasn't that far from the truth, btw.
> 
> But it isn't KASAN but GCOV profiling. Or is it KCOV profiling which
> clang does.
> 
> That thing adds some counting glue to native_write_cr4():
> 
> (my comments from the actual singlestepping in qemu start with '##' below)
> 
> 	movq	$__llvm_gcov_ctr.48+8, %rbx				##  mov    $0xffffffff8837d3c0,%rbx
> .LBB8_1:                                # %set_register
>                                         # =>This Inner Loop Header: Depth=1
> 
> 	jmp	.Ltmp42
> 	...
> 
> .Ltmp42:                                # Block address taken
> .LBB8_7:                                # %if.end79
>         movq    %rbx, %rax						## 0xffffffff8837d3c0
>         shrq    $3, %rax						## 0x1ffffffff106fa78
>         movabsq $-2305847407260205056, %rcx     # imm = 0xDFFFFC0000000000	## 0xdffffc0000000000
>         cmpb    $0, (%rax,%rcx)
>         je      .LBB8_9
> 
> so the memory address CMP accesses is something as nonsensical as
> 
>   0xfffffbfff106fa78
> 
> so I'm guessing we need to setup something for that __llvm_gcov_ctr to
> deref properly but I haven't dug deeper.
> 
> The important thing is that this triggers with clang-13 and -14. gcc is
> fine with the same config but that probably is because gcc does other
> profiling - gcov - I guess. Looking at the resulting asm, it has a bunch
> of those counter increments:
> 
>         incq    __gcov0.native_write_cr4+88(%rip)       # __gcov0.native_write_cr4[11]
> 
> but no weird memory references.
> 
> So, clang folks, what's up?
> 
> The fix is simple but I'd like to understand first why does this fail
> only with clang, 13 and newer.
> 
> (I mean, melver pointed me to
> 
>   380d53c45ff2 ("compiler_attributes.h: define __no_profile, add to noinstr")
> 
> which explains why 13 and newer).
> 
> Btw, joro, that second hunk is I think needed too because a couple of
> lines earlier we set up the cr4 shadow so I think you should use it
> instead of touching the hw CR4.
> 
> ---
> diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
> index 0083464de5e3..79b3d67addcc 100644
> --- a/arch/x86/kernel/cpu/common.c
> +++ b/arch/x86/kernel/cpu/common.c
> @@ -384,7 +384,7 @@ void native_write_cr0(unsigned long val)
>  }
>  EXPORT_SYMBOL(native_write_cr0);
>  
> -void native_write_cr4(unsigned long val)
> +void __no_profile native_write_cr4(unsigned long val)
>  {
>  	unsigned long bits_changed = 0;
>  
> diff --git a/arch/x86/kernel/head64.c b/arch/x86/kernel/head64.c
> index 75acb6027a87..68d2b7f9a913 100644
> --- a/arch/x86/kernel/head64.c
> +++ b/arch/x86/kernel/head64.c
> @@ -483,7 +483,7 @@ asmlinkage __visible void __init x86_64_start_kernel(char * real_mode_data)
>  	/* Kill off the identity-map trampoline */
>  	reset_early_page_tables();
>  
> -	__native_tlb_flush_global(native_read_cr4());
> +	__native_tlb_flush_global(this_cpu_read(cpu_tlbstate.cr4));
>  
>  	clear_bss();
>  
> 
> 
> Leaving in the rest for the newly added folks.
I tried this fix and it works fine in my local env. Will test it also in our
test box once we back to office. Thanks.

Regards
Yin, Fengwei

> 
>> If you don't want to use lkp tool to reproduce the issue, following command
>> could be used as well:
>>
>> Use Qemu command so only kernel image need be downloaded:
>> qemu-system-x86_64 -enable-kvm -cpu SandyBridge -smp 2 -m 16G -s -S -kernel vmlinuz-5.16.0-rc3-00003-gf154f290855b -nographic -append "console=ttyS0 earlyprintk=ttyS0,115200"
>> to reproduce it.
>>
>>
>>
>> Regards
>> Yin, Fengwei
>>
>>
>>
>>>>
>>>> I mean, if you cannot send me what I ask for, you can say so. Then I can
>>>> ignore this whole report altogether and waste my time somewhere else.
>>>
>>> We have uploaded vmlinuz, modules.cgz, config as well as other related file to:
>>> https://download.01.org/0day-ci/lkp-qemu/pkg/linux/x86_64-randconfig-a013-20211207/clang-14/f154f290855b070cc94dd44ad253c0ef8a9337bb/
>>>
>>> Machine types can refer to:
>>> https://zerobin.net/?e107cf7b56495d80#MQLh14wUT9Osv1tWCwiQx/okkAN48Nq+drVPE0PiNPw=
>>>
>>> If there's any other msg needed, pls feel free to propose, thanks.
>>>
>>> Below are our full steps to reproduce the issue:
>>>
>>> # download lkp-tests
>>> $ git clone https://github.com/intel/lkp-tests.git
>>>
>>> $ cd lkp-tests/
>>>
>>> # download vmlinuz
>>> $ wget https://download.01.org/0day-ci/lkp-qemu/pkg/linux/x86_64-randconfig-a013-20211207/clang-14/f154f290855b070cc94dd44ad253c0ef8a9337bb/vmlinuz-5.16.0-rc3-00003-gf154f290855b
>>>
>>> # dowmload modules.cgz
>>> $ wget https://download.01.org/0day-ci/lkp-qemu/pkg/linux/x86_64-randconfig-a013-20211207/clang-14/f154f290855b070cc94dd44ad253c0ef8a9337bb/modules.cgz
>>>
>>> # download job-script which is attached
>>>
>>> # run lkp qemu
>>> lkp-tests$ sudo bin/lkp qemu -k vmlinuz-5.16.0-rc3-00003-gf154f290855b -m modules.cgz job-script
>>>
>>> ~/lkp-tests/pkg/lkp-src ~/lkp-tests
>>> x86_64
>>> ==> Making package: lkp-src 0-1 (Thu 16 Dec 2021 07:26:22 PM CST)
>>> ==> Checking runtime dependencies...
>>> ==> Checking buildtime dependencies...
>>> ==> WARNING: Using existing $srcdir/ tree
>>> ==> Removing existing $pkgdir/ directory...
>>> ==> Starting build()...
>>> make: Entering directory '/home/carel/lkp-tests/bin/event'
>>> klcc  -D_FORTIFY_SOURCE=2  -c -o wakeup.o wakeup.c
>>> klcc  -Wl,-O1,--sort-common,--as-needed,-z,relro -static -o wakeup wakeup.o
>>> rm -f wakeup.o
>>> strip wakeup
>>> make: Leaving directory '/home/carel/lkp-tests/bin/event'
>>> ==> Entering fakeroot environment...
>>> x86_64
>>> ==> Starting package()...
>>> ==> Creating package "lkp-src"...
>>> 103987 blocks
>>> renamed '/home/carel/.lkp/cache/lkp-x86_64.cgz.tmp' -> '/home/carel/.lkp/cache/lkp-x86_64.cgz'
>>> ==> Leaving fakeroot environment.
>>> ==> Finished making: lkp-src 0-1 (Thu 16 Dec 2021 07:26:24 PM CST)
>>> ~/lkp-tests
>>> 12 blocks
>>> result_root: /home/carel/.lkp//result/boot/1/vm-snb/debian-10.4-x86_64-20200603.cgz/x86_64-randconfig-a013-20211207/clang-14/f154f290855b070cc94dd44ad253c0ef8a9337bb/0
>>> downloading initrds ...
>>> use local modules: /home/carel/.lkp/cache/modules.cgz
>>> /usr/bin/wget -q --timeout=1800 --tries=1 --local-encoding=UTF-8 http://0day.sh.intel.com:80/~lkp/osimage/debian/debian-10.4-x86_64-20200603.cgz -N -P /home/carel/.lkp/cache/osimage/debian
>>> 440459 blocks
>>> /usr/bin/wget -q --timeout=1800 --tries=1 --local-encoding=UTF-8 http://0day.sh.intel.com:80/~lkp/osimage/deps/debian-10.4-x86_64-20200603.cgz/run-ipconfig_20200608.cgz -N -P /home/carel/.lkp/cache/osimage/deps/debian-10.4-x86_64-20200603.cgz
>>> 1773 blocks
>>> /usr/bin/wget -q --timeout=1800 --tries=1 --local-encoding=UTF-8 http://0day.sh.intel.com:80/~lkp/osimage/deps/debian-10.4-x86_64-20200603.cgz/lkp_20210707.cgz -N -P /home/carel/.lkp/cache/osimage/deps/debian-10.4-x86_64-20200603.cgz
>>> 2321 blocks
>>> /usr/bin/wget -q --timeout=1800 --tries=1 --local-encoding=UTF-8 http://0day.sh.intel.com:80/~lkp/osimage/deps/debian-10.4-x86_64-20200603.cgz/rsync-rootfs_20200608.cgz -N -P /home/carel/.lkp/cache/osimage/deps/debian-10.4-x86_64-20200603.cgz
>>> 6856 blocks
>>> exec command: qemu-system-x86_64 -enable-kvm -fsdev local,id=test_dev,path=/home/carel/.lkp//result/boot/1/vm-snb/debian-10.4-x86_64-20200603.cgz/x86_64-randconfig-a013-20211207/clang-14/f154f290855b070cc94dd44ad253c0ef8a9337bb/0,security_model=none -device virtio-9p-pci,fsdev=test_dev,mount_tag=9p/virtfs_mount -kernel vmlinuz-5.16.0-rc3-00003-gf154f290855b -append root=/dev/ram0 user=lkp job=/lkp/jobs/scheduled/vm-snb-192/boot-1-debian-10.4-x86_64-20200603.cgz-f154f290855b070cc94dd44ad253c0ef8a9337bb-20211208-23538-lnvkeg-5.yaml ARCH=x86_64 kconfig=x86_64-randconfig-a013-20211207 branch=tip/x86/mm commit=f154f290855b070cc94dd44ad253c0ef8a9337bb BOOT_IMAGE=/pkg/linux/x86_64-randconfig-a013-20211207/clang-14/f154f290855b070cc94dd44ad253c0ef8a9337bb/vmlinuz-5.16.0-rc3-00003-gf154f290855b vmalloc=128M initramfs_async=0 page_owner=on max_uptime=600 RESULT_ROOT=/result/boot/1/vm-snb/debian-10.4-x86_64-20200603.cgz/x86_64-randconfig-a013-20211207/clang-14/f154f290855b070cc94dd44ad253c0ef8a9337bb/3 LKP_LOCAL_RUN=1 selinux=0 debug apic=debug sysrq_always_enabled rcupdate.rcu_cpu_stall_timeout=100 net.ifnames=0 printk.devkmsg=on panic=-1 softlockup_panic=1 nmi_watchdog=panic oops=panic load_ramdisk=2 prompt_ramdisk=0 drbd.minor_count=8 systemd.log_level=err ignore_loglevel console=tty0 earlyprintk=ttyS0,115200 console=ttyS0,115200 vga=normal rw  ip=dhcp result_service=9p/virtfs_mount -initrd /home/carel/.lkp/cache/final_initrd -smp 2 -m 3144M -no-reboot -watchdog i6300esb -rtc base=localtime -device e1000,netdev=net0 -netdev user,id=net0 -display none -monitor null -serial stdio
>>> early console in setup code
>>> early console in extract_kernel
>>> input_data: 0x0000000006ffc2e0
>>> input_len: 0x000000000260cb2b
>>> output: 0x0000000001000000
>>> output_len: 0x00000000079e7da4
>>> kernel_total_size: 0x0000000008a2c000
>>> needed_size: 0x0000000008c00000
>>> trampoline_32bit: 0x000000000009d000
>>> Physical KASLR using RDTSC...
>>> Virtual KASLR using RDTSC...
>>>
>>> Decompressing Linux... Parsing ELF... Performing relocations... done.
>>> Booting the kernel.
>>>
>>>>
>>>> -- 
>>>> Regards/Gruss,
>>>>     Boris.
>>>>
>>>> SUSE Software Solutions Germany GmbH, GF: Ivo Totev, HRB 36809, AG Nürnberg
> 

Re: [LKP] Re: [x86/mm/64] f154f29085: BUG:kernel_reboot-without-warning_in_boot_stage - clang KCOV?

[Borislav Petkov]

On Fri, Dec 17, 2021 at 11:04:13AM -0700, Nathan Chancellor wrote:
> This is GCOV, -fprofile-arcs.

Aha, and no_profile_instrument_function disables that.

> I am not reallys ure how exactly GCOV works under the hood so I cannot
> really comment on it (Nick might); it seems like llvm_gcov_init needs to
> get called for __llvm_gcov_ctr to get set up properly and maybe that
> hasn't happened at the point.

Hmm, right, there is a

        .p2align        4, 0x90                         # -- Begin function __llvm_gcov_init
        .type   __llvm_gcov_init,@function
__llvm_gcov_init:                       # @__llvm_gcov_init

in arch/x86/kernel/cpu/common.s which contains native_write_cr4() which does

	jmp     llvm_gcov_init@PLT

and that function is part of initcalls:

	.section	.init_array.0,"aw",@init_array
	.p2align	3
	.quad	__llvm_gcov_init
	.section	.init_array.1,"aw",@init_array
	.p2align	3
	.quad	asan.module_ctor
	.section	.fini_array.1,"aw",@fini_array
	.p2align	3
	.quad	asan.module_dtor
	.type	.L___asan_gen_.313,@object      # @___asan_gen_.313
	.section	.rodata.str1.1,"aMS",@progbits,1

which, AFAICT, gets called by kernel_init_freeable->do_basic_setup->do_ctors()

which is a lot later than x86_64_start_kernel() so I guess the
__no_profile tag for that function probably makes sense as a fix.

> This is a bit of a brain dump, apologies for not offering much upfront
> analysis, I am not as familiar with LLVM internals as Nick but this
> might help others look into the problem.

No, this is still highly appreciated - thanks for taking the time!

> I ended up seeing this thread yesterday through a lore filter that I
> have

Nice filtering. :-)

I did Cc llvm@lists.linux.dev in the hope that you guys would see it.

> and I bisected LLVM based on the fact that it happened with
> clang-13 but not clang-12; that bisect pointed out Nick's commit in LLVM
> that added the no profile attribute, which means that GCOV and KASAN
> need to be enabled to see this bug. I was not able to reproduce it with
> just one of them enabled at a time.

Ah, that's an interesting point:

$ grep -E "(GCOV|KASAN)" /tmp/config-5.16.0-rc3-00003-gf154f290855b | grep -v "^#"
CONFIG_KASAN_SHADOW_OFFSET=0xdffffc0000000000
CONFIG_GCOV_KERNEL=y
CONFIG_ARCH_HAS_GCOV_PROFILE_ALL=y
CONFIG_GCOV_PROFILE_ALL=y
CONFIG_HAVE_ARCH_KASAN=y
CONFIG_HAVE_ARCH_KASAN_VMALLOC=y
CONFIG_CC_HAS_KASAN_GENERIC=y
CONFIG_CC_HAS_KASAN_SW_TAGS=y
CONFIG_KASAN=y
CONFIG_KASAN_GENERIC=y
CONFIG_KASAN_INLINE=y
CONFIG_KASAN_VMALLOC=y

> With that, I removed the no profile attribute dependency on GCOV_KERNEL
> and bisected again, landing on the commit in LLVM 13 that enables the
> new pass manager, which fundamentally changes how LLVM transforms its
> IR. Whenever that has happened in the past, it usually points to a
> pre-existing issue; if I go back to clang-11 (the current minimum of
> -next) and enable the NPM there with -fexperimental-new-pass-manager, I
> see this hang so it seems like there might be some issue how GCOV and
> KASAN are manipulated together in the context of the NPM that was not
> present with the legacy pass manager.

Aha, so it used to work, apparently. Or the NPM is adding additional
code which needs to be initialized because it works ok after the
constructors have run.

> I do see tests in LLVM that test to make sure __llvm_gcov_ctr does not
> get instrumented with KASAN, maybe there is another interaction that
> should not be happening between those two?

Right.

Ok, thanks for the insights, let's see what Nick figures out here.

Thx.

-- 
Regards/Gruss,
    Boris.

SUSE Software Solutions Germany GmbH, GF: Ivo Totev, HRB 36809, AG Nürnberg

Re: [LKP] Re: [x86/mm/64] f154f29085: BUG:kernel_reboot-without-warning_in_boot_stage - clang KCOV?

[Borislav Petkov]

On Sat, Dec 18, 2021 at 06:39:46PM +0800, Yin Fengwei wrote:
> Thanks a lot for sharing this. Lessons learnt here. Will follow this
> rule exactly in the future.

Thanks. And for the future, please trim your reply like I just did. :)

> I tried this fix and it works fine in my local env. Will test it also
> in our test box once we back to office. Thanks.

Good, much appreciated.

Thx.

-- 
Regards/Gruss,
    Boris.

SUSE Software Solutions Germany GmbH, GF: Ivo Totev, HRB 36809, AG Nürnberg

Re: [LKP] Re: [x86/mm/64] f154f29085: BUG:kernel_reboot-without-warning_in_boot_stage - clang KCOV?

[Yin Fengwei]

On 12/18/21 7:01 PM, Borislav Petkov wrote:
> On Sat, Dec 18, 2021 at 06:39:46PM +0800, Yin Fengwei wrote:
>> Thanks a lot for sharing this. Lessons learnt here. Will follow this
>> rule exactly in the future.
> 
> Thanks. And for the future, please trim your reply like I just did. :)
Sure. Thanks.

> 
>> I tried this fix and it works fine in my local env. Will test it also
>> in our test box once we back to office. Thanks.
> 
> Good, much appreciated.
It's our pleasure. Carel will send out the official test report on our
test box.

Regards
Yin, Fengwei

> 
> Thx.
> 

[PATCH] x86/mm: Prevent early boot triple-faults with instrumentation

[Borislav Petkov]

From: Borislav Petkov <bp@suse.de>

Commit in Fixes added a global TLB flush on the early boot path, after
the kernel switches off of the trampoline page table.

Compiler profiling options add additional measurement code
which needs to be initialized prior to use. The global flush in
x86_64_start_kernel() happens before those initializations can happen,
leading to accessing invalid memory.

The second issue this fixes is with KASAN: for a similar reason,
kasan_early_init() needs to have happened before KASAN-instrumented
functions are called.

Therefore, reorder the flush to happen after the KASAN early init
and prevent the compilers from adding profiling instrumentation to
native_write_cr4().

Fixes: f154f290855b ("x86/mm/64: Flush global TLB on boot and AP bringup")
Reported-by: "J. Bruce Fields" <bfields@fieldses.org>
Reported-by: kernel test robot <oliver.sang@intel.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lore.kernel.org/r/20211209144141.GC25654@xsang-OptiPlex-9020
---
 arch/x86/kernel/cpu/common.c |  2 +-
 arch/x86/kernel/head64.c     | 16 ++++++++++++++--
 2 files changed, 15 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index 0083464de5e3..79b3d67addcc 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -384,7 +384,7 @@ void native_write_cr0(unsigned long val)
 }
 EXPORT_SYMBOL(native_write_cr0);
 
-void native_write_cr4(unsigned long val)
+void __no_profile native_write_cr4(unsigned long val)
 {
 	unsigned long bits_changed = 0;
 
diff --git a/arch/x86/kernel/head64.c b/arch/x86/kernel/head64.c
index 75acb6027a87..f5e80a8377ad 100644
--- a/arch/x86/kernel/head64.c
+++ b/arch/x86/kernel/head64.c
@@ -483,10 +483,12 @@ asmlinkage __visible void __init x86_64_start_kernel(char * real_mode_data)
 	/* Kill off the identity-map trampoline */
 	reset_early_page_tables();
 
-	__native_tlb_flush_global(native_read_cr4());
-
 	clear_bss();
 
+	/*
+	 * This needs to happen *before* kasan_early_init() because latter maps stuff
+	 * into that page.
+	 */
 	clear_page(init_top_pgt);
 
 	/*
@@ -498,6 +500,16 @@ asmlinkage __visible void __init x86_64_start_kernel(char * real_mode_data)
 
 	kasan_early_init();
 
+	/*
+	 * Flush global TLB entries which could be left over from the trampoline page
+	 * table.
+	 *
+	 * This needs to happen *after* kasan_early_init() as KASAN-enabled .configs
+	 * instrument native_write_cr4() so KASAN must be initialized for that
+	 * instrumentation to work.
+	 */
+	__native_tlb_flush_global(this_cpu_read(cpu_tlbstate.cr4));
+
 	idt_setup_early_handler();
 
 	copy_bootdata(__va(real_mode_data));
-- 
2.29.2

-- 
Regards/Gruss,
    Boris.

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

Re: [LKP] Re: [x86/mm/64] f154f29085: BUG:kernel_reboot-without-warning_in_boot_stage - clang KCOV?

[Carel Si]

Hi Boris,

On Fri, Dec 17, 2021 at 08:52:53PM +0800, Borislav Petkov wrote:
> ---
> diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
> index 0083464de5e3..79b3d67addcc 100644
> --- a/arch/x86/kernel/cpu/common.c
> +++ b/arch/x86/kernel/cpu/common.c
> @@ -384,7 +384,7 @@ void native_write_cr0(unsigned long val)
>  }
>  EXPORT_SYMBOL(native_write_cr0);
>  
> -void native_write_cr4(unsigned long val)
> +void __no_profile native_write_cr4(unsigned long val)
>  {
>  	unsigned long bits_changed = 0;
>  
> diff --git a/arch/x86/kernel/head64.c b/arch/x86/kernel/head64.c
> index 75acb6027a87..68d2b7f9a913 100644
> --- a/arch/x86/kernel/head64.c
> +++ b/arch/x86/kernel/head64.c
> @@ -483,7 +483,7 @@ asmlinkage __visible void __init x86_64_start_kernel(char * real_mode_data)
>  	/* Kill off the identity-map trampoline */
>  	reset_early_page_tables();
>  
> -	__native_tlb_flush_global(native_read_cr4());
> +	__native_tlb_flush_global(this_cpu_read(cpu_tlbstate.cr4));
>  
>  	clear_bss();
>  

We tested your patch, it can fix the issue, thanks.

=========================================================================================
compiler/kconfig/rootfs/sleep/tbox_group/testcase:
  clang-14/x86_64-randconfig-a013-20211207/debian-10.4-x86_64-20200603.cgz/1/vm-snb/boot

commit: 
  9de4999050 ("x86/realmode: Add comment for Global bit usage in trampoline_pgd")
  f154f29085 ("x86/mm/64: Flush global TLB on boot and AP bringup") 
  d12ddfe498 ("fixup-for-f154f29085")

9de4999050b5f2e8 f154f290855b070cc94dd44ad25 d12ddfe498329a0967c008d8183 
---------------- --------------------------- --------------------------- 
       fail:runs  %reproduction    fail:runs  %reproduction    fail:runs
           |             |             |             |             |    
           :27         100%          27:27           0%            :27    dmesg.BUG:kernel_reboot-without-warning_in_boot_stage

Re: [LKP] Re: [x86/mm/64] f154f29085: BUG:kernel_reboot-without-warning_in_boot_stage - clang KCOV?

[Marco Elver]

On Tue, 21 Dec 2021 at 15:34, Carel Si <beibei.si@intel.com> wrote:
>
> Hi Boris,
>
> On Fri, Dec 17, 2021 at 08:52:53PM +0800, Borislav Petkov wrote:
> > ---
> > diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
> > index 0083464de5e3..79b3d67addcc 100644
> > --- a/arch/x86/kernel/cpu/common.c
> > +++ b/arch/x86/kernel/cpu/common.c
> > @@ -384,7 +384,7 @@ void native_write_cr0(unsigned long val)
> >  }
> >  EXPORT_SYMBOL(native_write_cr0);
> >
> > -void native_write_cr4(unsigned long val)
> > +void __no_profile native_write_cr4(unsigned long val)
> >  {
> >       unsigned long bits_changed = 0;
> >
> > diff --git a/arch/x86/kernel/head64.c b/arch/x86/kernel/head64.c
> > index 75acb6027a87..68d2b7f9a913 100644
> > --- a/arch/x86/kernel/head64.c
> > +++ b/arch/x86/kernel/head64.c
> > @@ -483,7 +483,7 @@ asmlinkage __visible void __init x86_64_start_kernel(char * real_mode_data)
> >       /* Kill off the identity-map trampoline */
> >       reset_early_page_tables();
> >
> > -     __native_tlb_flush_global(native_read_cr4());
> > +     __native_tlb_flush_global(this_cpu_read(cpu_tlbstate.cr4));
> >
> >       clear_bss();

Also double-check the Makefile-based solution: the Makefiles in both
directories already contain various KCOV_INSTRUMENT/K*SAN_SANITIZE :=
n, so perhaps adding GCOV_PROFILE or GCOV_PROFILE_whicheverfile.o := n
may be more appropriate should the functions that should not be
instrumented be a moving target, and prone to breakage again in
future.

Re: [LKP] Re: [x86/mm/64] f154f29085: BUG:kernel_reboot-without-warning_in_boot_stage - clang KCOV?

[Borislav Petkov]

On Tue, Dec 21, 2021 at 10:31:54PM +0800, Carel Si wrote:
> We tested your patch, it can fix the issue, thanks.

You mean "it does fix the issue". :-)

Thanks for testing, I'll add your Tested-by.

-- 
Regards/Gruss,
    Boris.

SUSE Software Solutions Germany GmbH, GF: Ivo Totev, HRB 36809, AG Nürnberg

Re: [LKP] Re: [x86/mm/64] f154f29085: BUG:kernel_reboot-without-warning_in_boot_stage - clang KCOV?

[Borislav Petkov]

On Tue, Dec 21, 2021 at 04:10:31PM +0100, Marco Elver wrote:
> Also double-check the Makefile-based solution: the Makefiles in both
> directories already contain various KCOV_INSTRUMENT/K*SAN_SANITIZE :=
> n, so perhaps adding GCOV_PROFILE or GCOV_PROFILE_whicheverfile.o := n
> may be more appropriate should the functions that should not be
> instrumented be a moving target, and prone to breakage again in
> future.

Yeah, I asked whether we should exclude the whole ...cpu/common.c from
profiling - it has mostly init code so it probably doesn't matter
for coverage but no one said anything so I left it to the function
annotation.

And also, I'm still waiting on clang folks to chime in on the New Pass
Manager and whether there's a bug in clang there so that we won't need
the __no_profile annotation at all. I mean, gcc is fine with that config
so unless clang is doing more profiling gunk than gcc and requires that
__llvm_gcov_init constructor... see Nathan's mail upthread.

Thx.

-- 
Regards/Gruss,
    Boris.

SUSE Software Solutions Germany GmbH, GF: Ivo Totev, HRB 36809, AG Nürnberg

Re: [LKP] Re: [x86/mm/64] f154f29085: BUG:kernel_reboot-without-warning_in_boot_stage - clang KCOV?

[Yin Fengwei]

Hi Boris,

On 12/21/21 11:22 PM, Borislav Petkov wrote:
> And also, I'm still waiting on clang folks to chime in on the New Pass
> Manager and whether there's a bug in clang there so that we won't need
> the __no_profile annotation at all. I mean, gcc is fine with that config
> so unless clang is doing more profiling gunk than gcc and requires that
> __llvm_gcov_init constructor... see Nathan's mail upthread.

Did you get update from clang folks for this behavior? Thanks.


Regards
Yin, Fengwei

Re: [LKP] Re: [x86/mm/64] f154f29085: BUG:kernel_reboot-without-warning_in_boot_stage - clang KCOV?

[Borislav Petkov]

On Wed, Jan 05, 2022 at 10:35:20AM +0800, Yin Fengwei wrote:
> Did you get update from clang folks for this behavior? Thanks.

No. Why?

-- 
Regards/Gruss,
    Boris.

SUSE Software Solutions Germany GmbH, GF: Ivo Totev, HRB 36809, AG Nürnberg

Re: [LKP] Re: [x86/mm/64] f154f29085: BUG:kernel_reboot-without-warning_in_boot_stage - clang KCOV?

[Yin Fengwei]

On 1/5/2022 7:36 PM, Borislav Petkov wrote:
> On Wed, Jan 05, 2022 at 10:35:20AM +0800, Yin Fengwei wrote:
>> Did you get update from clang folks for this behavior? Thanks.
> 
> No. Why?
My understanding:
it's better that clang restore its behavior to clang-12. Or people
need to use __no_profile annotation if want to add function before
GCOV/KASAN is initialized. Thanks.


Regards
Yin, Fengwei

> 

Re: [LKP] Re: [x86/mm/64] f154f29085: BUG:kernel_reboot-without-warning_in_boot_stage - clang KCOV?

[Borislav Petkov]

On Wed, Jan 05, 2022 at 08:47:28PM +0800, Yin Fengwei wrote:
> it's better that clang restore its behavior to clang-12.

Probably, but I'm not gonna hold my breath - folks are likely very
busy...

> Or people need to use __no_profile annotation if want to add function
> before GCOV/KASAN is initialized.

... yap, and because fixing it this way is easy, I've already queued the
__no_profile solution:

https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git/commit/?h=x86/mm&id=b64dfcde1ca9cb82e38e573753f0c0db8fb841c2

Thanks.

-- 
Regards/Gruss,
    Boris.

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

Re: [LKP] Re: [x86/mm/64] f154f29085: BUG:kernel_reboot-without-warning_in_boot_stage - clang KCOV?

[Yin Fengwei]

Hi Boris,

On 1/5/22 11:21 PM, Borislav Petkov wrote:
> ... yap, and because fixing it this way is easy, I've already queued the
> __no_profile solution:
> 
> https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git/commit/?h=x86/mm&id=b64dfcde1ca9cb82e38e573753f0c0db8fb841c2
This fixing is good to me.

Just a little concern: if people need to add function in the future,
if he/she is not using clang-14, it's possible that he/she misses the
__no_profile and triggers this kind of issue again.

It may not be a big problem (we will capture it in our test. :)). Thanks.


Regards
Yin, Fengwei

> 
> Thanks.