From: Andrew Cooper <andrew.cooper3@citrix.com>
To: Jan Beulich <JBeulich@suse.com>,
xen-devel <xen-devel@lists.xenproject.org>
Cc: Wei Liu <wei.liu2@citrix.com>
Subject: Re: [PATCH] x86: refine debugging of SMEP/SMAP fix
Date: Tue, 17 May 2016 11:28:26 +0100 [thread overview]
Message-ID: <573AF24A.3000407@citrix.com> (raw)
In-Reply-To: <573B067302000078000EC093@prv-mh.provo.novell.com>
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On 17/05/16 10:54, Jan Beulich wrote:
> Instead of just latching cr4_pv32_mask into %rdx, correct the found
> wrong value in %cr4 (to avoid triggering another BUG). The value left
> in %rdx should be sufficient for deducing cr4_pv32_mask from the
> register dump.
Alternatively, you can reuse %rax (as its value is useless by this
point) and leave %rdx as exactly cr4_pv32_mask. This avoids needing a
subsequent step to reverse engineer cr4_pv32_mask.
>
> Also there is one more place for XEN_CR4_PV32_BITS to be used.
So there is. Sorry for missing it.
~Andrew
>
> Signed-off-by: Jan Beulich <jbeulich@suse.com>
>
> --- a/xen/arch/x86/x86_64/compat/entry.S
> +++ b/xen/arch/x86/x86_64/compat/entry.S
> @@ -182,7 +182,7 @@ ENTRY(compat_restore_all_guest)
> testb $3,UREGS_cs(%rsp)
> jpe .Lcr4_alt_end
> mov CPUINFO_cr4-CPUINFO_guest_cpu_user_regs(%rsp), %rax
> - and $~(X86_CR4_SMEP|X86_CR4_SMAP), %rax
> + and $~XEN_CR4_PV32_BITS, %rax
> mov %rax, CPUINFO_cr4-CPUINFO_guest_cpu_user_regs(%rsp)
> mov %rax, %cr4
> .Lcr4_alt_end:
> @@ -218,8 +218,10 @@ ENTRY(cr4_pv32_restore)
> and cr4_pv32_mask(%rip), %rax
> cmp cr4_pv32_mask(%rip), %rax
> je 1f
> - /* Cause cr4_pv32_mask to be visible in the BUG register dump. */
> - mov cr4_pv32_mask(%rip), %rdx
> + /* Avoid coming back here while handling the #UD we cause below. */
> + mov %cr4, %rdx
> + or cr4_pv32_mask(%rip), %rdx
> + mov %rdx, %cr4
> BUG
> 1:
> #endif
>
>
>
>
>
> _______________________________________________
> Xen-devel mailing list
> Xen-devel@lists.xen.org
> http://lists.xen.org/xen-devel
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next prev parent reply other threads:[~2016-05-17 10:28 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-05-17 9:54 [PATCH] x86: refine debugging of SMEP/SMAP fix Jan Beulich
2016-05-17 10:28 ` Andrew Cooper [this message]
2016-05-17 10:42 ` Jan Beulich
2016-05-17 12:56 ` Andrew Cooper
2016-05-17 13:04 ` Jan Beulich
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