[v4] riscv: Allow to downgrade paging mode from the command line

[PATCH v4 0/1] riscv: Allow to downgrade paging mode from the command line

Posted by Alexandre Ghiti 3 years ago

This new version gets rid of the limitation that prevented KASAN kernels
to use the newly introduced parameters.

While looking into KASLR, I fell onto commit aacd149b6238 ("arm64: head:
avoid relocating the kernel twice for KASLR"): it allows to use the fdt
functions very early in the boot process with KASAN enabled by simply
compiling a new version of those functions without instrumentation.

I had to change the handling of the command line parsing to make the
code self-contained in kernel/pi/cmd_early.c to avoid calling too many
__pi prefixed functions from outside this file.

I'll use this approach like arm64 to handle the extraction of the random
seedi from the device tree for KASLR.

@Ard: I copied the "pi" name but I have to admit I don't know what it
means.

Alexandre Ghiti (1):
  riscv: Allow to downgrade paging mode from the command line

 .../admin-guide/kernel-parameters.txt         |  5 +-
 arch/riscv/kernel/Makefile                    |  2 +
 arch/riscv/kernel/pi/Makefile                 | 34 ++++++++++++
 arch/riscv/kernel/pi/cmdline_early.c          | 52 +++++++++++++++++++
 arch/riscv/lib/memcpy.S                       |  2 +
 arch/riscv/lib/memmove.S                      |  2 +
 arch/riscv/mm/init.c                          | 36 ++++++++++---
 7 files changed, 126 insertions(+), 7 deletions(-)
 create mode 100644 arch/riscv/kernel/pi/Makefile
 create mode 100644 arch/riscv/kernel/pi/cmdline_early.c

-- 
2.37.2

Re: [PATCH v4 0/1] riscv: Allow to downgrade paging mode from the command line

Posted by Björn Töpel 2 years, 11 months ago

Alexandre Ghiti <alexghiti@rivosinc.com> writes:

> This new version gets rid of the limitation that prevented KASAN kernels
> to use the newly introduced parameters.
>
> While looking into KASLR, I fell onto commit aacd149b6238 ("arm64: head:
> avoid relocating the kernel twice for KASLR"): it allows to use the fdt
> functions very early in the boot process with KASAN enabled by simply
> compiling a new version of those functions without instrumentation.
>
> I had to change the handling of the command line parsing to make the
> code self-contained in kernel/pi/cmd_early.c to avoid calling too many
> __pi prefixed functions from outside this file.
>
> I'll use this approach like arm64 to handle the extraction of the random
> seedi from the device tree for KASLR.
>
> @Ard: I copied the "pi" name but I have to admit I don't know what it
> means.

__pi_ is for "position-independent" -- KASLR related.

For the (tiny ;-)) series:

Tested-by: Björn Töpel <bjorn@rivosinc.com>
Reviewed-by: Björn Töpel <bjorn@rivosinc.com>

Re: [PATCH v4 0/1] riscv: Allow to downgrade paging mode from the command line

Posted by Conor Dooley 3 years ago

Hey Alex,

On Tue, Jan 31, 2023 at 04:11:14PM +0100, Alexandre Ghiti wrote:
> This new version gets rid of the limitation that prevented KASAN kernels
> to use the newly introduced parameters.

What's the base commit for this version?
Fails to apply for me on top of for-next, fixes, rc1, and linux-next :/
I also tried it on top of your KASAN series, but no luck there either!

Thanks,
Conor.

> While looking into KASLR, I fell onto commit aacd149b6238 ("arm64: head:
> avoid relocating the kernel twice for KASLR"): it allows to use the fdt
> functions very early in the boot process with KASAN enabled by simply
> compiling a new version of those functions without instrumentation.
> 
> I had to change the handling of the command line parsing to make the
> code self-contained in kernel/pi/cmd_early.c to avoid calling too many
> __pi prefixed functions from outside this file.
> 
> I'll use this approach like arm64 to handle the extraction of the random
> seedi from the device tree for KASLR.
> 
> @Ard: I copied the "pi" name but I have to admit I don't know what it
> means.
> 
> Alexandre Ghiti (1):
>   riscv: Allow to downgrade paging mode from the command line
> 
>  .../admin-guide/kernel-parameters.txt         |  5 +-
>  arch/riscv/kernel/Makefile                    |  2 +
>  arch/riscv/kernel/pi/Makefile                 | 34 ++++++++++++
>  arch/riscv/kernel/pi/cmdline_early.c          | 52 +++++++++++++++++++
>  arch/riscv/lib/memcpy.S                       |  2 +
>  arch/riscv/lib/memmove.S                      |  2 +
>  arch/riscv/mm/init.c                          | 36 ++++++++++---
>  7 files changed, 126 insertions(+), 7 deletions(-)
>  create mode 100644 arch/riscv/kernel/pi/Makefile
>  create mode 100644 arch/riscv/kernel/pi/cmdline_early.c
> 
> -- 
> 2.37.2
>

Re: [PATCH v4 0/1] riscv: Allow to downgrade paging mode from the command line

Posted by Alexandre Ghiti 3 years ago

Hi Conor,

On Tue, Jan 31, 2023 at 8:25 PM Conor Dooley <conor@kernel.org> wrote:
>
> Hey Alex,
>
> On Tue, Jan 31, 2023 at 04:11:14PM +0100, Alexandre Ghiti wrote:
> > This new version gets rid of the limitation that prevented KASAN kernels
> > to use the newly introduced parameters.
>
> What's the base commit for this version?
> Fails to apply for me on top of for-next, fixes, rc1, and linux-next :/
> I also tried it on top of your KASAN series, but no luck there either!

Really sorry about that, that's the second time it happens, I'll
improve my workflow: I'll include the base-commit sha1/tag + a link to
all needed-but-not-yet-upstreamed patches.

Thanks for your time,

Alex

>
> Thanks,
> Conor.
>
> > While looking into KASLR, I fell onto commit aacd149b6238 ("arm64: head:
> > avoid relocating the kernel twice for KASLR"): it allows to use the fdt
> > functions very early in the boot process with KASAN enabled by simply
> > compiling a new version of those functions without instrumentation.
> >
> > I had to change the handling of the command line parsing to make the
> > code self-contained in kernel/pi/cmd_early.c to avoid calling too many
> > __pi prefixed functions from outside this file.
> >
> > I'll use this approach like arm64 to handle the extraction of the random
> > seedi from the device tree for KASLR.
> >
> > @Ard: I copied the "pi" name but I have to admit I don't know what it
> > means.
> >
> > Alexandre Ghiti (1):
> >   riscv: Allow to downgrade paging mode from the command line
> >
> >  .../admin-guide/kernel-parameters.txt         |  5 +-
> >  arch/riscv/kernel/Makefile                    |  2 +
> >  arch/riscv/kernel/pi/Makefile                 | 34 ++++++++++++
> >  arch/riscv/kernel/pi/cmdline_early.c          | 52 +++++++++++++++++++
> >  arch/riscv/lib/memcpy.S                       |  2 +
> >  arch/riscv/lib/memmove.S                      |  2 +
> >  arch/riscv/mm/init.c                          | 36 ++++++++++---
> >  7 files changed, 126 insertions(+), 7 deletions(-)
> >  create mode 100644 arch/riscv/kernel/pi/Makefile
> >  create mode 100644 arch/riscv/kernel/pi/cmdline_early.c
> >
> > --
> > 2.37.2
> >

Re: [PATCH v4 0/1] riscv: Allow to downgrade paging mode from the command line

Posted by Alexandre Ghiti 3 years ago

On Thu, Feb 2, 2023 at 4:07 PM Alexandre Ghiti <alexghiti@rivosinc.com> wrote:
>
> Hi Conor,
>
> On Tue, Jan 31, 2023 at 8:25 PM Conor Dooley <conor@kernel.org> wrote:
> >
> > Hey Alex,
> >
> > On Tue, Jan 31, 2023 at 04:11:14PM +0100, Alexandre Ghiti wrote:
> > > This new version gets rid of the limitation that prevented KASAN kernels
> > > to use the newly introduced parameters.
> >
> > What's the base commit for this version?

And to answer your question: this patch applies nicely on top of
v6.2-rc6 + my KASAN patchset
(https://patchwork.kernel.org/project/linux-riscv/list/?series=715388)

> > Fails to apply for me on top of for-next, fixes, rc1, and linux-next :/
> > I also tried it on top of your KASAN series, but no luck there either!
>
> Really sorry about that, that's the second time it happens, I'll
> improve my workflow: I'll include the base-commit sha1/tag + a link to
> all needed-but-not-yet-upstreamed patches.
>
> Thanks for your time,
>
> Alex
>
> >
> > Thanks,
> > Conor.
> >
> > > While looking into KASLR, I fell onto commit aacd149b6238 ("arm64: head:
> > > avoid relocating the kernel twice for KASLR"): it allows to use the fdt
> > > functions very early in the boot process with KASAN enabled by simply
> > > compiling a new version of those functions without instrumentation.
> > >
> > > I had to change the handling of the command line parsing to make the
> > > code self-contained in kernel/pi/cmd_early.c to avoid calling too many
> > > __pi prefixed functions from outside this file.
> > >
> > > I'll use this approach like arm64 to handle the extraction of the random
> > > seedi from the device tree for KASLR.
> > >
> > > @Ard: I copied the "pi" name but I have to admit I don't know what it
> > > means.
> > >
> > > Alexandre Ghiti (1):
> > >   riscv: Allow to downgrade paging mode from the command line
> > >
> > >  .../admin-guide/kernel-parameters.txt         |  5 +-
> > >  arch/riscv/kernel/Makefile                    |  2 +
> > >  arch/riscv/kernel/pi/Makefile                 | 34 ++++++++++++
> > >  arch/riscv/kernel/pi/cmdline_early.c          | 52 +++++++++++++++++++
> > >  arch/riscv/lib/memcpy.S                       |  2 +
> > >  arch/riscv/lib/memmove.S                      |  2 +
> > >  arch/riscv/mm/init.c                          | 36 ++++++++++---
> > >  7 files changed, 126 insertions(+), 7 deletions(-)
> > >  create mode 100644 arch/riscv/kernel/pi/Makefile
> > >  create mode 100644 arch/riscv/kernel/pi/cmdline_early.c
> > >
> > > --
> > > 2.37.2
> > >

Re: [PATCH v4 0/1] riscv: Allow to downgrade paging mode from the command line

Posted by Alexandre Ghiti 3 years ago

Sorry, I forgot the changelog again:

|v4: - Remove the kasan limitation by compiling 'local' fdt functions, 
as done in arm64 by Ard - Remove RB from Björn as the cmdline handling 
changed v3: - Massage commit log to make no4lvl clearer, as asked by 
Conor - Add a note to kernel-parameters.txt regarding the impossibility 
to use those parameters when KASAN is enabled, as suggested by Conor - 
Add RB from Björn v2: - Honor CMDLINE_EXTEND and CMDLINE_FORCE as 
noticed by Björn|

On 1/31/23 16:11, Alexandre Ghiti wrote:
> This new version gets rid of the limitation that prevented KASAN kernels
> to use the newly introduced parameters.
>
> While looking into KASLR, I fell onto commit aacd149b6238 ("arm64: head:
> avoid relocating the kernel twice for KASLR"): it allows to use the fdt
> functions very early in the boot process with KASAN enabled by simply
> compiling a new version of those functions without instrumentation.
>
> I had to change the handling of the command line parsing to make the
> code self-contained in kernel/pi/cmd_early.c to avoid calling too many
> __pi prefixed functions from outside this file.
>
> I'll use this approach like arm64 to handle the extraction of the random
> seedi from the device tree for KASLR.
>
> @Ard: I copied the "pi" name but I have to admit I don't know what it
> means.
>
> Alexandre Ghiti (1):
>    riscv: Allow to downgrade paging mode from the command line
>
>   .../admin-guide/kernel-parameters.txt         |  5 +-
>   arch/riscv/kernel/Makefile                    |  2 +
>   arch/riscv/kernel/pi/Makefile                 | 34 ++++++++++++
>   arch/riscv/kernel/pi/cmdline_early.c          | 52 +++++++++++++++++++
>   arch/riscv/lib/memcpy.S                       |  2 +
>   arch/riscv/lib/memmove.S                      |  2 +
>   arch/riscv/mm/init.c                          | 36 ++++++++++---
>   7 files changed, 126 insertions(+), 7 deletions(-)
>   create mode 100644 arch/riscv/kernel/pi/Makefile
>   create mode 100644 arch/riscv/kernel/pi/cmdline_early.c
>