From: "Roger Pau Monné" <roger.pau@citrix.com>
To: Jan Beulich <jbeulich@suse.com>
Cc: "xen-devel@lists.xenproject.org" <xen-devel@lists.xenproject.org>,
Wei Liu <wl@xen.org>, Andrew Cooper <andrew.cooper3@citrix.com>
Subject: Re: [PATCH 2/4] x86: reduce CET-SS related #ifdef-ary
Date: Mon, 27 Jul 2020 17:00:02 +0200 [thread overview]
Message-ID: <20200727150002.GS7191@Air-de-Roger> (raw)
In-Reply-To: <58615a18-7f81-c000-d499-1a49f4752879@suse.com>
On Wed, Jul 15, 2020 at 12:48:46PM +0200, Jan Beulich wrote:
> Commit b586a81b7a90 ("x86/CET: Fix build following c/s 43b98e7190") had
> to introduce a number of #ifdef-s to make the build work with older tool
> chains. Introduce an assembler macro covering for tool chains not
> knowing of CET-SS, allowing some conditionals where just SETSSBSY is the
> problem to be dropped again.
>
> No change to generated code.
>
> Signed-off-by: Jan Beulich <jbeulich@suse.com>
Looks like an improvement overall in code clarity:
Reviewed-by: Roger Pau Monné <roger.pau@citrix.com>
Can you test on clang? Just to be on the safe side, otherwise I can
test it.
> ---
> Now that I've done this I'm not longer sure which direction is better to
> follow: On one hand this introduces dead code (even if just NOPs) into
> CET-SS-disabled builds. Otoh this is a step towards breaking the tool
> chain version dependency of the feature.
>
> I've also dropped conditionals around bigger chunks of code; while I
> think that's preferable, I'm open to undo those parts.
>
> --- a/xen/arch/x86/boot/x86_64.S
> +++ b/xen/arch/x86/boot/x86_64.S
> @@ -31,7 +31,6 @@ ENTRY(__high_start)
> jz .L_bsp
>
> /* APs. Set up shadow stacks before entering C. */
> -#ifdef CONFIG_XEN_SHSTK
> testl $cpufeat_mask(X86_FEATURE_XEN_SHSTK), \
> CPUINFO_FEATURE_OFFSET(X86_FEATURE_XEN_SHSTK) + boot_cpu_data(%rip)
> je .L_ap_shstk_done
> @@ -55,7 +54,6 @@ ENTRY(__high_start)
> mov $XEN_MINIMAL_CR4 | X86_CR4_CET, %ecx
> mov %rcx, %cr4
> setssbsy
> -#endif
>
> .L_ap_shstk_done:
> call start_secondary
> --- a/xen/arch/x86/setup.c
> +++ b/xen/arch/x86/setup.c
> @@ -668,7 +668,7 @@ static void __init noreturn reinit_bsp_s
> stack_base[0] = stack;
> memguard_guard_stack(stack);
>
> - if ( IS_ENABLED(CONFIG_XEN_SHSTK) && cpu_has_xen_shstk )
> + if ( cpu_has_xen_shstk )
> {
> wrmsrl(MSR_PL0_SSP,
> (unsigned long)stack + (PRIMARY_SHSTK_SLOT + 1) * PAGE_SIZE - 8);
> --- a/xen/arch/x86/x86_64/compat/entry.S
> +++ b/xen/arch/x86/x86_64/compat/entry.S
> @@ -198,9 +198,7 @@ ENTRY(cr4_pv32_restore)
>
> /* See lstar_enter for entry register state. */
> ENTRY(cstar_enter)
> -#ifdef CONFIG_XEN_SHSTK
> ALTERNATIVE "", "setssbsy", X86_FEATURE_XEN_SHSTK
> -#endif
> /* sti could live here when we don't switch page tables below. */
> CR4_PV32_RESTORE
> movq 8(%rsp),%rax /* Restore %rax. */
> --- a/xen/arch/x86/x86_64/entry.S
> +++ b/xen/arch/x86/x86_64/entry.S
> @@ -237,9 +237,7 @@ iret_exit_to_guest:
> * %ss must be saved into the space left by the trampoline.
> */
> ENTRY(lstar_enter)
> -#ifdef CONFIG_XEN_SHSTK
> ALTERNATIVE "", "setssbsy", X86_FEATURE_XEN_SHSTK
Should the setssbsy be quoted, or it doesn't matter? I'm asking
because the same construction used by CLAC/STAC doesn't quote the
instruction.
Roger.
next prev parent reply other threads:[~2020-07-27 15:00 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-07-15 10:47 [PATCH 0/4] x86: some assembler macro rework Jan Beulich
2020-07-15 10:48 ` [PATCH 1/4] x86: replace __ASM_{CL,ST}AC Jan Beulich
2020-07-27 14:55 ` Roger Pau Monné
2020-07-27 19:47 ` Jan Beulich
2020-07-28 9:06 ` Roger Pau Monné
2020-07-31 8:05 ` Jan Beulich
2020-07-31 8:12 ` Roger Pau Monné
2020-07-28 13:59 ` Andrew Cooper
2020-07-28 19:24 ` Jan Beulich
2020-07-28 13:55 ` Andrew Cooper
2020-07-28 19:18 ` Jan Beulich
2020-07-31 8:00 ` Jan Beulich
2020-07-15 10:48 ` [PATCH 2/4] x86: reduce CET-SS related #ifdef-ary Jan Beulich
2020-07-27 15:00 ` Roger Pau Monné [this message]
2020-07-27 19:50 ` Jan Beulich
2020-07-28 8:36 ` Roger Pau Monné
2020-07-28 14:29 ` Andrew Cooper
2020-07-28 19:33 ` Jan Beulich
2020-07-15 10:49 ` [PATCH 3/4] x86: drop ASM_{CL,ST}AC Jan Beulich
2020-07-27 15:10 ` Roger Pau Monné
2020-07-28 14:51 ` Andrew Cooper
2020-07-28 19:41 ` Jan Beulich
2020-07-15 10:49 ` [PATCH 4/4] x86: fold indirect_thunk_asm.h into asm-defns.h Jan Beulich
2020-07-27 15:16 ` Roger Pau Monné
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