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Re: [PATCH v5 32/32] x86/mm: Add support to make use of Secure Memory Encryption

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  Re: [PATCH v5 32/32] x86/mm: Add support to make use of Secure  Memory Encryption Borislav Petkov <bp@alien8.de> - 2017-05-19 13:40 +0200
    Re: [PATCH v5 32/32] x86/mm: Add support to make use of Secure  Memory Encryption Josh Poimboeuf <jpoimboe@redhat.com> - 2017-05-19 22:20 +0200
      Re: [PATCH v5 32/32] x86/mm: Add support to make use of Secure  Memory Encryption Borislav Petkov <bp@alien8.de> - 2017-05-19 22:40 +0200

#1645543 — Re: [PATCH v5 32/32] x86/mm: Add support to make use of Secure Memory Encryption

On Fri, Apr 21, 2017 at 01:56:13PM -0500, Tom Lendacky wrote:
> On 4/18/2017 4:22 PM, Tom Lendacky wrote:
> > Add support to check if SME has been enabled and if memory encryption
> > should be activated (checking of command line option based on the
> > configuration of the default state).  If memory encryption is to be
> > activated, then the encryption mask is set and the kernel is encrypted
> > "in place."
> > 
> > Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
> > ---
> >  arch/x86/kernel/head_64.S |    1 +
> >  arch/x86/mm/mem_encrypt.c |   83 +++++++++++++++++++++++++++++++++++++++++++--
> >  2 files changed, 80 insertions(+), 4 deletions(-)
> > 
> 
> ...
> 
> > 
> > -unsigned long __init sme_enable(void)
> > +unsigned long __init sme_enable(struct boot_params *bp)
> >  {
> > +	const char *cmdline_ptr, *cmdline_arg, *cmdline_on, *cmdline_off;
> > +	unsigned int eax, ebx, ecx, edx;
> > +	unsigned long me_mask;
> > +	bool active_by_default;
> > +	char buffer[16];
> 
> So it turns out that when KASLR is enabled (CONFIG_RAMDOMIZE_BASE=y)
> the stack-protector support causes issues with this function because

What issues?

> it is called so early. I can get past it by adding:
> 
> CFLAGS_mem_encrypt.o := $(nostackp)
> 
> in the arch/x86/mm/Makefile, but that obviously eliminates the support
> for the whole file.  Would it be better to split out the sme_enable()
> and other boot routines into a separate file or just apply the
> $(nostackp) to the whole file?

Josh might have a better idea here... CCed.

-- 
Regards/Gruss,
    Boris.

Good mailing practices for 400: avoid top-posting and trim the reply.

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#1645892

On Fri, May 19, 2017 at 01:30:05PM +0200, Borislav Petkov wrote:
> > it is called so early. I can get past it by adding:
> > 
> > CFLAGS_mem_encrypt.o := $(nostackp)
> > 
> > in the arch/x86/mm/Makefile, but that obviously eliminates the support
> > for the whole file.  Would it be better to split out the sme_enable()
> > and other boot routines into a separate file or just apply the
> > $(nostackp) to the whole file?
> 
> Josh might have a better idea here... CCed.

I'm the stack validation guy, not the stack protection guy :-)

But there is a way to disable compiler options on a per-function basis
with the gcc __optimize__ function attribute.  For example:

  __attribute__((__optimize__("no-stack-protector")))

-- 
Josh

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#1645908

On Fri, May 19, 2017 at 03:16:51PM -0500, Josh Poimboeuf wrote:
> I'm the stack validation guy, not the stack protection guy :-)

LOL. I thought you were *the* stacks guy. :-)))

But once you've validated it, you could protect it then too. :-)

-- 
Regards/Gruss,
    Boris.

Good mailing practices for 400: avoid top-posting and trim the reply.

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