From: Deepak Gupta <debug@rivosinc.com>
To: Charles Mirabile <cmirabil@redhat.com>
Cc: pjw@kernel.org, Liam.Howlett@oracle.com, a.hindborg@kernel.org,
akpm@linux-foundation.org, alex.gaynor@gmail.com,
alexghiti@rivosinc.com, aliceryhl@google.com,
alistair.francis@wdc.com, andybnac@gmail.com,
aou@eecs.berkeley.edu, arnd@arndb.de, atishp@rivosinc.com,
bjorn3_gh@protonmail.com, boqun.feng@gmail.com, bp@alien8.de,
brauner@kernel.org, broonie@kernel.org, charlie@rivosinc.com,
cleger@rivosinc.com, conor+dt@kernel.org, conor@kernel.org,
corbet@lwn.net, dave.hansen@linux.intel.com, david@redhat.com,
devicetree@vger.kernel.org, ebiederm@xmission.com,
evan@rivosinc.com, gary@garyguo.net, hpa@zytor.com,
jannh@google.com, jim.shu@sifive.com, kees@kernel.org,
kito.cheng@sifive.com, krzk+dt@kernel.org,
linux-arch@vger.kernel.org, linux-doc@vger.kernel.org,
linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
linux-kselftest@vger.kernel.org, linux-mm@kvack.org,
linux-riscv@lists.infradead.org, lorenzo.stoakes@oracle.com,
lossin@kernel.org, mingo@redhat.com, ojeda@kernel.org,
oleg@redhat.com, palmer@dabbelt.com, paul.walmsley@sifive.com,
peterz@infradead.org, richard.henderson@linaro.org,
rick.p.edgecombe@intel.com, robh@kernel.org,
rust-for-linux@vger.kernel.org, samitolvanen@google.com,
shuah@kernel.org, tglx@linutronix.de, tmgross@umich.edu,
vbabka@suse.cz, x86@kernel.org, zong.li@sifive.com
Subject: Re: [PATCH v19 00/27] riscv control-flow integrity for usermode
Date: Fri, 26 Sep 2025 12:57:40 -0700 [thread overview]
Message-ID: <aNbwNN_st4bxwdwx@debug.ba.rivosinc.com> (raw)
In-Reply-To: <20250926192919.349578-1-cmirabil@redhat.com>
Hi Charles,
Thanks for response. Rest inline
On Fri, Sep 26, 2025 at 03:29:19PM -0400, Charles Mirabile wrote:
>Hi -
>
>Hoping that I got everything right with git-send-email so that this is
>delivered alright...
>
>Wanted to jump in to head off a potential talking past one another /
>miscommunication situation I see here.
>
>On Wed, Sep 24, 2025 at 08:36:11AM -0600, Paul Walmsley wrote:
>> Hi,
>>
>> On Thu, 31 Jul 2025, Deepak Gupta wrote:
>>
>> [ ... ]
>>
>> > vDSO related Opens (in the flux)
>> > =================================
>> >
>> > I am listing these opens for laying out plan and what to expect in future
>> > patch sets. And of course for the sake of discussion.
>> >
>>
>> [ ... ]
>>
>> > How many vDSOs
>> > ---------------
>> > Shadow stack instructions are carved out of zimop (may be operations) and if CPU
>> > doesn't implement zimop, they're illegal instructions. Kernel could be running on
>> > a CPU which may or may not implement zimop. And thus kernel will have to carry 2
>> > different vDSOs and expose the appropriate one depending on whether CPU implements
>> > zimop or not.
>>
>> If we merge this series without this, then when CFI is enabled in the
>> Kconfig, we'll wind up with a non-portable kernel that won't run on older
>> hardware. We go to great lengths to enable kernel binary portability
>> across the presence or absence of other RISC-V extensions, and I think
>> these CFI extensions should be no different.
>
>That is not true, this series does not contain the VDSO changes so it can
>be merged as is.
Look at patch 23/27. It does have vDSO change. Although shadow stack
instruction are inserted as compiled flag for vDSO only when cfi config is
selected by user. Right now default is "No". So it won't impact anyone unles
user explicitly says "Yes".
>
>>
>> So before considering this for merging, I'd like to see at least an
>> attempt to implement the dual-vDSO approach (or something equivalent)
>> where the same kernel binary with CFI enabled can run on both pre-Zimop
>> and post-Zimop hardware, with the existing userspaces that are common
>> today.
>
>I agree that when the VDSO patches are submitted for inclusion they should
>be written in a way that avoids limiting the entire kernel to either
>pre-Zimop or post-Zimop hardware based on the config, but I think it
>should be quite possible to perform e.g. runtime patching of the VDSO
>to replace the Zimop instructions with nops if the config is enabled but
>the hardware does not support Zimop.
Why kernel need to do this extra work of carry two binaries and patching it
runtime?
If for instance we do this, and then this allow this kernel to be taken to
pre-Zimop hardware, it is assumed that entire userspace for such hardware
was compiled without shadow stack (thus no zimop). In that case, kernel
should have been compiled without CFI option.
Just for sake of thought exercise, let's say Fedora 43 is first release with
RVA23 compatiblity (zimop and shadow stack), there is no way this and future
release will be able to run on pre-zimop hardware. Unless redhat is going to
start two different binary distribution. One for pre-zimop and one for
post-zimop. If that would be the case, then compiling two different kernel for
such two different hardware would be least of the worry.
Only other usecase is of a seasoned kernel developer or build your own stuff
in embedded environment, those users can anyways are advanced users. But it
forces complexity on rest of kernel. There will be more extensions taking zimop
encodings in future, we will end up patching vDSO and keep this complexity
while rest of the userspace will not be patched and will be separate binary
distribution (if OS distros endup distributing multiple binaries per release)
>
>However, that concern should not hold up this patch series. Raise it again
>when the VDSO patches are posted.
As I said earlier, these changes default cfi config to No. So whenever this
is selected "Yes" by a distro, they can drive such patches (if there is a real
need)
>
>>
>> thanks Deepak,
>>
>> - Paul
>
>Best - Charlie
>
next prev parent reply other threads:[~2025-09-26 19:57 UTC|newest]
Thread overview: 51+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-07-31 23:19 [PATCH v19 00/27] riscv control-flow integrity for usermode Deepak Gupta
2025-07-31 23:19 ` [PATCH v19 01/27] mm: VM_SHADOW_STACK definition for riscv Deepak Gupta
2025-07-31 23:19 ` [PATCH v19 02/27] dt-bindings: riscv: zicfilp and zicfiss in dt-bindings (extensions.yaml) Deepak Gupta
2025-07-31 23:19 ` [PATCH v19 03/27] riscv: zicfiss / zicfilp enumeration Deepak Gupta
2025-07-31 23:19 ` [PATCH v19 04/27] riscv: zicfiss / zicfilp extension csr and bit definitions Deepak Gupta
2025-07-31 23:19 ` [PATCH v19 05/27] riscv: usercfi state for task and save/restore of CSR_SSP on trap entry/exit Deepak Gupta
2025-07-31 23:19 ` [PATCH v19 06/27] riscv/mm : ensure PROT_WRITE leads to VM_READ | VM_WRITE Deepak Gupta
2025-07-31 23:19 ` [PATCH v19 07/27] riscv/mm: manufacture shadow stack pte Deepak Gupta
2025-07-31 23:19 ` [PATCH v19 08/27] riscv/mm: teach pte_mkwrite to manufacture shadow stack PTEs Deepak Gupta
2025-07-31 23:19 ` [PATCH v19 09/27] riscv/mm: write protect and shadow stack Deepak Gupta
2025-07-31 23:19 ` [PATCH v19 10/27] riscv/mm: Implement map_shadow_stack() syscall Deepak Gupta
2025-07-31 23:19 ` [PATCH v19 11/27] riscv/shstk: If needed allocate a new shadow stack on clone Deepak Gupta
2025-07-31 23:19 ` [PATCH v19 12/27] riscv: Implements arch agnostic shadow stack prctls Deepak Gupta
2025-07-31 23:19 ` [PATCH v19 13/27] prctl: arch-agnostic prctl for indirect branch tracking Deepak Gupta
2025-07-31 23:19 ` [PATCH v19 14/27] riscv: Implements arch agnostic indirect branch tracking prctls Deepak Gupta
2025-07-31 23:19 ` [PATCH v19 15/27] riscv/traps: Introduce software check exception and uprobe handling Deepak Gupta
2025-07-31 23:19 ` [PATCH v19 16/27] riscv: signal: abstract header saving for setup_sigcontext Deepak Gupta
2025-07-31 23:19 ` [PATCH v19 17/27] riscv/signal: save and restore of shadow stack for signal Deepak Gupta
2025-07-31 23:19 ` [PATCH v19 18/27] riscv/kernel: update __show_regs to print shadow stack register Deepak Gupta
2025-07-31 23:19 ` [PATCH v19 19/27] riscv/ptrace: riscv cfi status and state via ptrace and in core files Deepak Gupta
2025-07-31 23:19 ` [PATCH v19 20/27] riscv/hwprobe: zicfilp / zicfiss enumeration in hwprobe Deepak Gupta
2025-07-31 23:19 ` [PATCH v19 21/27] riscv: kernel command line option to opt out of user cfi Deepak Gupta
2025-07-31 23:19 ` [PATCH v19 22/27] riscv: enable kernel access to shadow stack memory via FWFT sbi call Deepak Gupta
2025-07-31 23:19 ` [PATCH v19 23/27] arch/riscv: compile vdso with landing pad and shadow stack note Deepak Gupta
2025-07-31 23:19 ` [PATCH v19 24/27] riscv: create a config for shadow stack and landing pad instr support Deepak Gupta
2025-07-31 23:19 ` [PATCH v19 25/27] riscv: Documentation for landing pad / indirect branch tracking Deepak Gupta
2025-07-31 23:19 ` [PATCH v19 26/27] riscv: Documentation for shadow stack on riscv Deepak Gupta
2025-07-31 23:19 ` [PATCH v19 27/27] kselftest/riscv: kselftest for user mode cfi Deepak Gupta
2025-08-01 1:09 ` [PATCH v19 00/27] riscv control-flow integrity for usermode Benjamin LaHaise
2025-08-06 17:15 ` patchwork-bot+linux-riscv
2025-08-07 12:28 ` Mark Brown
2025-08-08 8:23 ` Deepak Gupta
2025-08-08 11:48 ` Mark Brown
2025-08-08 17:20 ` Deepak Gupta
2025-09-24 14:36 ` Paul Walmsley
2025-09-24 18:40 ` Deepak Gupta
2025-09-25 12:30 ` Andy Chiu
2025-09-25 14:30 ` Deepak Gupta
2025-09-30 11:15 ` Florian Weimer
2025-10-01 0:13 ` Deepak Gupta
2025-09-26 19:29 ` Charles Mirabile
2025-09-26 19:52 ` Charles Mirabile
2025-09-26 20:03 ` Deepak Gupta
2025-09-26 19:57 ` Deepak Gupta [this message]
2025-09-26 20:28 ` Charles Mirabile
2025-09-26 21:07 ` Deepak Gupta
2025-09-30 9:20 ` Florian Weimer
2025-09-30 23:48 ` Deepak Gupta
2025-10-02 11:45 ` Florian Weimer
2025-10-02 16:45 ` Deepak Gupta
2025-10-13 14:30 ` Florian Weimer
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=aNbwNN_st4bxwdwx@debug.ba.rivosinc.com \
--to=debug@rivosinc.com \
--cc=Liam.Howlett@oracle.com \
--cc=a.hindborg@kernel.org \
--cc=akpm@linux-foundation.org \
--cc=alex.gaynor@gmail.com \
--cc=alexghiti@rivosinc.com \
--cc=aliceryhl@google.com \
--cc=alistair.francis@wdc.com \
--cc=andybnac@gmail.com \
--cc=aou@eecs.berkeley.edu \
--cc=arnd@arndb.de \
--cc=atishp@rivosinc.com \
--cc=bjorn3_gh@protonmail.com \
--cc=boqun.feng@gmail.com \
--cc=bp@alien8.de \
--cc=brauner@kernel.org \
--cc=broonie@kernel.org \
--cc=charlie@rivosinc.com \
--cc=cleger@rivosinc.com \
--cc=cmirabil@redhat.com \
--cc=conor+dt@kernel.org \
--cc=conor@kernel.org \
--cc=corbet@lwn.net \
--cc=dave.hansen@linux.intel.com \
--cc=david@redhat.com \
--cc=devicetree@vger.kernel.org \
--cc=ebiederm@xmission.com \
--cc=evan@rivosinc.com \
--cc=gary@garyguo.net \
--cc=hpa@zytor.com \
--cc=jannh@google.com \
--cc=jim.shu@sifive.com \
--cc=kees@kernel.org \
--cc=kito.cheng@sifive.com \
--cc=krzk+dt@kernel.org \
--cc=linux-arch@vger.kernel.org \
--cc=linux-doc@vger.kernel.org \
--cc=linux-fsdevel@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-kselftest@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=linux-riscv@lists.infradead.org \
--cc=lorenzo.stoakes@oracle.com \
--cc=lossin@kernel.org \
--cc=mingo@redhat.com \
--cc=ojeda@kernel.org \
--cc=oleg@redhat.com \
--cc=palmer@dabbelt.com \
--cc=paul.walmsley@sifive.com \
--cc=peterz@infradead.org \
--cc=pjw@kernel.org \
--cc=richard.henderson@linaro.org \
--cc=rick.p.edgecombe@intel.com \
--cc=robh@kernel.org \
--cc=rust-for-linux@vger.kernel.org \
--cc=samitolvanen@google.com \
--cc=shuah@kernel.org \
--cc=tglx@linutronix.de \
--cc=tmgross@umich.edu \
--cc=vbabka@suse.cz \
--cc=x86@kernel.org \
--cc=zong.li@sifive.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).