ACK: [PATCH] UBUNTU: SAUCE: TDX: Work around the segfault issue in glibc 2.35 in Ubuntu 22.04.

[Ian May]

LGTM

Acked-by: Ian May <ian.may at canonical.com>

On 2023-01-23 07:02:33 , Tim Gardner wrote:
> From: Dexuan Cui <decui at microsoft.com>
> 
> BugLink: https://bugs.launchpad.net/bugs/2003714
> 
> glibc 2.34/2.35 (and 2.36?) had a bug (2.32 is good):
> See https://sourceware.org/bugzilla/show_bug.cgi?id=28784
> 
> The bug has been fixed in upstream glibc:
> https://sourceware.org/git/?p=glibc.git;a=commitdiff;h=c242fcce06e3102ca663b2f992611d0bda4f2668
> 
> However, it looks like a lot of distros haven't picked up the fix yet,
> e.g. Ubuntu 22.04/22.10/23.04's glibc need pick up the glibc fix (c242fcce06e3102ca663b2f992611d0bda4f2668).
> RHEL 9's glibc needs the glibc fix as well.
> 
> Before the glibc packages in the distros are fixed, we can use this
> kernel side workaround patch for now. The workaround is from Intel.
> See the below for the rationale:
> 
> x86/tdx: Virtualize CPUID leaf 0x2
> CPUID leaf 0x2 provides cache and TLB information. In TDX guest access
> to the leaf causes #VE.
> 
> Current implementation returns all zero, but it confuses some users:
> some recent versions of GLIBC hit segfaults. It is a GLIBC bug, but it is
> also a user-visible regression comparing to non-TDX environment.
> 
> Kernel can generate a sensible response to the #VE to work around the
> glibc segfault for now.
> 
> The leaf is obsolete. There are leafs that provides the same
> information in a structured form. See leaf 0x4 on cache info and
> leaf 0x18 on TLB info.
> 
> Generate a response that indicates that CPUID leaf 0x4 and 0x18 have to
> be used instead.
> 
> (cherry picked from commit 16218cf73491e867fd39c16c9e4b8aa926cbda68 https://github.com/dcui/tdx)
> Signed-off-by: Tim Gardner <tim.gardner at canonical.com>
> ---
>  arch/x86/coco/tdx/tdx.c | 12 ++++++++++++
>  1 file changed, 12 insertions(+)
> 
> diff --git a/arch/x86/coco/tdx/tdx.c b/arch/x86/coco/tdx/tdx.c
> index c32c7ef55249..928ca748bb26 100644
> --- a/arch/x86/coco/tdx/tdx.c
> +++ b/arch/x86/coco/tdx/tdx.c
> @@ -329,6 +329,18 @@ static int handle_cpuid(struct pt_regs *regs, struct ve_info *ve)
>  		.r13 = regs->cx,
>  	};
>  
> +	/*
> +	 * Work around the segfault issue in glibc 2.35 in Ubuntu 22.04.
> +	 * See https://sourceware.org/bugzilla/show_bug.cgi?id=28784
> +	 * Ubuntu 22.04/22.10/23.04's glibc should pick up this glibc fix:
> +	 * https://sourceware.org/git/?p=glibc.git;a=commitdiff;h=c242fcce06e3102ca663b2f992611d0bda4f2668
> +	 */
> +	if (regs->ax == 2) {
> +		regs->ax = 0xf1ff01;
> +		regs->bx = regs->cx = regs->dx = 0;
> +		return ve_instr_len(ve);
> +	}
> +
>  	/*
>  	 * Only allow VMM to control range reserved for hypervisor
>  	 * communication.
> -- 
> 2.34.1
> 
> 
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