Re: [PATCH 5.18 000/231] 5.18.13-rc1 review

[Jiri Slaby <jirislaby@kernel.org>]

On 20. 07. 22, 19:28, Linus Torvalds wrote:
> [ Adding PeterZ and Jiri to the participants. ]
> 
> Looks like 5.18.13 added that commit 9bb2ec608a20 ("objtool: Update
> Retpoline validation") but I don't see 3131ef39fb03 ("x86/asm/32: Fix
> ANNOTATE_UNRET_SAFE use on 32-bit") in that list.
> 
> That said, 3131ef39fb03 should have fixed a completely different issue
> on 32-bit, not the "naked ret" thing.

Right. After applying 3131ef39fb03 on the top of 5.18.12 (or 5.18.13-rc1 
too), I'm fine:
https://build.opensuse.org/public/build/Kernel:stable/standard/i586/kernel-pae/_log

I.e. no warnings at all, the kernel compiles and runs fine -- tested in 
qemu only. It's gcc12 as can be seen in the log above.

Config:
https://github.com/openSUSE/kernel-source/blob/stable/config/i386/pae

It says:
CONFIG_CC_HAS_SLS=y
CONFIG_CC_HAS_RETURN_THUNK=y
CONFIG_SPECULATION_MITIGATIONS=y
CONFIG_PAGE_TABLE_ISOLATION=y
CONFIG_RETPOLINE=y
CONFIG_RETHUNK=y
CONFIG_CPU_UNRET_ENTRY=y
CONFIG_CPU_IBPB_ENTRY=y
CONFIG_CPU_IBRS_ENTRY=y
CONFIG_ARCH_MHP_MEMMAP_ON_MEMORY_ENABLE=y

Patches:
https://github.com/openSUSE/kernel-source/tree/stable/patches.suse

Apart from others, it contains:
3131ef39fb03 x86/asm/32: Fix ANNOTATE_UNRET_SAFE use on 32-bit
bb06650634d3 KVM: VMX: Convert launched argument to flags
bea7e31a5cac KVM: VMX: Fix IBRS handling after vmexit
8bd200d23ec4 KVM: VMX: Flatten __vmx_vcpu_run()
07853adc29a0 KVM: VMX: Prevent RSB underflow before vmenter
fc02735b14ff KVM: VMX: Prevent guest RSB poisoning attacks with eIBRS
bf5835bcdb96 intel_idle: Disable IBRS during long idle
a09a6e2399ba objtool: Add entry UNRET validation
8faea26e6111 objtool: Re-add UNWIND_HINT_{SAVE_RESTORE}
951ddecf4356 objtool: Treat .text.__x86.* as noinstr
9bb2ec608a20 objtool: Update Retpoline validation
a149180fbcf3 x86: Add magic AMD return-thunk
15e67227c49a x86: Undo return-thunk damage
aa3d480315ba x86: Use return-thunk in asm code
d77cfe594ad5 x86/bpf: Use alternative RET encoding
7fbf47c7ce50 x86/bugs: Add AMD retbleed= boot parameter
f54d45372c6a x86/bugs: Add Cannon lake to RETBleed affected CPU list
3ebc17006888 x86/bugs: Add retbleed=ibpb
0fe4aeea9c01 x86/bugs: Do IBPB fallback check only once
2259da159fbe x86/bugs: Do not enable IBPB-on-entry when IBPB is not 
supported
e8ec1b6e08a2 x86/bugs: Enable STIBP for JMP2RET
caa0ff24d5d0 x86/bugs: Keep a per-CPU IA32_SPEC_CTRL value
c779bc1a9002 x86/bugs: Optimize SPEC_CTRL MSR writes
bcf163150cd3 x86/bugs: Remove apostrophe typo
6b80b59b3555 x86/bugs: Report AMD retbleed vulnerability
6ad0ad2bf8a6 x86/bugs: Report Intel retbleed vulnerability
166115c08a9b x86/bugs: Split spectre_v2_select_mitigation() and 
spectre_v2_user_select_mitigation()
7a05bc95ed1c x86/common: Stamp out the stepping madness
d7caac991fee x86/cpu/amd: Add Spectral Chicken
26aae8ccbc19 x86/cpu/amd: Enumerate BTC_NO
a883d624aed4 x86/cpufeatures: Move RETPOLINE flags to word 11
2dbb887e875b x86/entry: Add kernel IBRS implementation
7c81c0c9210c x86/entry: Avoid very early RET
64cbd0acb582 x86/entry: Don't call error_entry() for XENPV
2c08b9b38f5b x86/entry: Move PUSH_AND_CLEAR_REGS() back into error_entry
ee774dac0da1 x86/entry: Move PUSH_AND_CLEAR_REGS out of error_entry()
d16e0b266720 x86/entry: Remove UNTRAIN_RET from native_irq_return_ldt
1b331eeea7b8 x86/entry: Remove skip_r11rcx
520a7e80c96d x86/entry: Switch the stack after error_entry() returns
1f001e9da6bb x86/ftrace: Use alternative RET encoding
697977d8415d x86/kexec: Disable RET on kexec
af2e140f3420 x86/kvm: Fix SETcc emulation for return thunks
84e7051c0bc1 x86/kvm: fix FASTOP_SIZE when return thunks are enabled
742ab6df974a x86/kvm/vmx: Make noinstr clean
a1e2c031ec39 x86/mm: Simplify RESERVE_BRK()
d9e9d2300681 x86,objtool: Create .return_sites
f43b9876e857 x86/retbleed: Add fine grained Kconfig knobs
369ae6ffc41a x86/retpoline: Cleanup some #ifdefery
00e1533325fd x86/retpoline: Swizzle retpoline thunk
0b53c374b9ef x86/retpoline: Use -mfunction-return
0ee9073000e8 x86/sev: Avoid using __x86_return_thunk
7c693f54c873 x86/speculation: Add spectre_v2=ibrs option to support 
Kernel IBRS
4ad3278df6fe x86/speculation: Disable RRSBA behavior
9756bba28470 x86/speculation: Fill RSB on vmexit for IBRS
b2620facef48 x86/speculation: Fix RSB filling with CONFIG_RETPOLINE=n
56aa4d221f1e x86/speculation: Fix SPEC_CTRL write on SMT state change
e6aa13622ea8 x86/speculation: Fix firmware entry SPEC_CTRL handling
acac5e98ef8d x86/speculation: Remove x86_spec_ctrl_mask
bbb69e8bee1b x86/speculation: Use cached host SPEC_CTRL value for guest 
entry/exit
c27c753ea6fd x86/static_call: Serialize __static_call_fixup() properly
ee88d363d156 x86,static_call: Use alternative RET encoding
0aca53c6b522 x86/traps: Use pt_regs directly in fixup_bad_iret()
15583e514eb1 x86/vsyscall_emu/64: Don't use RET in vsyscall emulation
d147553b64ba x86/xen: Add UNTRAIN_RET
b75b7f8ef114 x86/xen: Rename SYS* entry points

Series file:
https://github.com/openSUSE/kernel-source/blob/stable/series.conf

> PeterZ, Jiri, any ideas? Limited quoting below, see thread at
> 
>    https://lore.kernel.org/all/CA+G9fYsJBBbEXowA-3kxDNqcfbtcqmxBrEnJSkCnLUsMzNfJZw@mail.gmail.com/
> 
> for more details.
> 
>                Linus
> 
> On Wed, Jul 20, 2022 at 9:37 AM Justin Forbes <jforbes@fedoraproject.org> wrote:
>>
>> On Tue, Jul 19, 2022 at 12:32:48PM -0700, Linus Torvalds wrote:
>>> On Tue, Jul 19, 2022 at 10:57 AM Naresh Kamboju
>>> <naresh.kamboju@linaro.org> wrote:
>>>>
>>>>
>>>> 2. Large number of build warnings on x86 with gcc-11,
>>>> I do not see these build warnings on mainline,
>>> ..
>>>> 'naked' return found in RETPOLINE build
>>>
>>> Hmm. Does your cross-compiler support '-mfunction-return=thunk-extern'?
>>>
>>> Your build does magic things with 'scripts/kconfig/merge_config.sh',
>>> and I'm wondering if you perhaps end up enabling CONFIG_RETHUNK with a
>>> compiler that doesn't actually support it, or something like that?
>>
>> I am seeing these 'naked' return found in RETPOLINE build on the
>> standard fedora 36 toolchain as well. No cross compiling, nothing fancy.
>> These were not seen with mainline, or with the 5.18.12-rc1 retbleed
>> patches.
>>
>> Justin

regards,
-- 
js
suse labs