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Date: Thu, 20 Oct 2022 16:30:26 +0300 From: Evgeniy Baskov <baskov@...ras.ru> To: Andrew Cooper <Andrew.Cooper3@...rix.com> Cc: Ard Biesheuvel <ardb@...nel.org>, Borislav Petkov <bp@...en8.de>, Andy Lutomirski <luto@...nel.org>, Dave Hansen <dave.hansen@...ux.intel.com>, Ingo Molnar <mingo@...hat.com>, Peter Zijlstra <peterz@...radead.org>, Thomas Gleixner <tglx@...utronix.de>, Alexey Khoroshilov <khoroshilov@...ras.ru>, lvc-project@...uxtesting.org, x86@...nel.org, linux-efi@...r.kernel.org, linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org Subject: Re: [PATCH 06/16] x86/boot: Setup memory protection for bzImage code On 2022-10-19 10:57, Andrew Cooper wrote: > On 06/09/2022 11:41, Evgeniy Baskov wrote: >> diff --git a/arch/x86/boot/compressed/head_64.S >> b/arch/x86/boot/compressed/head_64.S >> index 5273367283b7..889ca7176aa7 100644 >> --- a/arch/x86/boot/compressed/head_64.S >> +++ b/arch/x86/boot/compressed/head_64.S >> @@ -602,6 +603,28 @@ SYM_FUNC_START_LOCAL_NOALIGN(.Lrelocated) >> jmp *%rax >> SYM_FUNC_END(.Lrelocated) >> >> +SYM_FUNC_START_LOCAL_NOALIGN(startup32_enable_nx_if_supported) >> + pushq %rbx >> + >> + leaq has_nx(%rip), %rcx >> + >> + mov $0x80000001, %eax >> + cpuid >> + btl $20, %edx > > btl $(X86_FEATURE_NX & 31), %edx > > But also need to check for the availability of the extended leaf in the > first place. Yes, thank you for suggestion, that looks more readable. I will also add the leaf node check. Is there any processor though that supports long mode and does not support 0x80000001 leaf node? > >> + jnc .Lnonx >> + >> + movl $1, (%rcx) > > Your pointer has been clobbered with some feature flags. Thanks, I apparently forgot to include fix for this into a patch set... > > movl $1, has_nx(%rip) > > will work fine without needing the intermediary lea. > > ~Andrew
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