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Message-ID: <zvqilmzjja2writdqrjutnoszjkjiio3zk5jcbcxmw2s7rvx2i@mdwzolbmgwzz>
Date: Thu, 24 Oct 2024 17:09:49 +0300
From: "Kirill A. Shutemov" <kirill@...temov.name>
To: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
x86@...nel.org, Andrew Cooper <andrew.cooper3@...rix.com>,
Josh Poimboeuf <jpoimboe@...nel.org>, Borislav Petkov <bp@...en8.de>
Subject: Re: [PATCH] x86: fix user address masking non-canonical speculation
issue
On Wed, Oct 23, 2024 at 06:31:59PM -0700, Linus Torvalds wrote:
> diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
> index f1040cb64841..d671f78f658e 100644
> --- a/arch/x86/kernel/cpu/common.c
> +++ b/arch/x86/kernel/cpu/common.c
> @@ -69,6 +69,7 @@
> #include <asm/sev.h>
> #include <asm/tdx.h>
> #include <asm/posted_intr.h>
> +#include <asm/runtime-const.h>
>
> #include "cpu.h"
>
> @@ -2389,6 +2390,15 @@ void __init arch_cpu_finalize_init(void)
> alternative_instructions();
>
> if (IS_ENABLED(CONFIG_X86_64)) {
> + unsigned long USER_PTR_MAX = TASK_SIZE_MAX;
> +
> + /*
> + * Enable this when LAM is gated on LASS support
> + if (cpu_feature_enabled(X86_FEATURE_LAM))
> + USER_PTR_MAX = (1ul << 63) - PAGE_SIZE;
> + */
It will be safe to uncomment it once the patch in tip/x86/urgent gets
merged[1]. We clear X86_FEATURE_LAM if kernel is compiled without LAM.
[1] https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git/commit/?h=x86/urgent&id=3267cb6d3a174ff83d6287dcd5b0047bbd912452
> + runtime_const_init(ptr, USER_PTR_MAX);
> +
> /*
> * Make sure the first 2MB area is not mapped by huge pages
> * There are typically fixed size MTRRs in there and overlapping
> diff --git a/arch/x86/lib/getuser.S b/arch/x86/lib/getuser.S
> index d066aecf8aeb..4357ec2a0bfc 100644
> --- a/arch/x86/lib/getuser.S
> +++ b/arch/x86/lib/getuser.S
> @@ -39,8 +39,13 @@
>
> .macro check_range size:req
> .if IS_ENABLED(CONFIG_X86_64)
> - mov %rax, %rdx
> - sar $63, %rdx
> + movq $0x0123456789abcdef,%rdx
> + 1:
> + .pushsection runtime_ptr_USER_PTR_MAX,"a"
> + .long 1b - 8 - .
> + .popsection
> + cmp %rax, %rdx
> + sbb %rdx, %rdx
> or %rdx, %rax
> .else
> cmp $TASK_SIZE_MAX-\size+1, %eax
Maybe worth adding assembly macro for the runtime_ptr?
diff --git a/arch/x86/include/asm/runtime-const.h b/arch/x86/include/asm/runtime-const.h
index 24e3a53ca255..563566f361f7 100644
--- a/arch/x86/include/asm/runtime-const.h
+++ b/arch/x86/include/asm/runtime-const.h
@@ -2,6 +2,18 @@
#ifndef _ASM_RUNTIME_CONST_H
#define _ASM_RUNTIME_CONST_H
+#ifdef __ASSEMBLY__
+
+.macro RUNTIME_CONST_PTR sym reg
+ movq $0x0123456789abcdef, %\reg
+ 1:
+ .pushsection runtime_ptr_\sym, "a"
+ .long 1b - 8 - .
+ .popsection
+.endm
+
+#else /* __ASSEMBLY__ */
+
#define runtime_const_ptr(sym) ({ \
typeof(sym) __ret; \
asm_inline("mov %1,%0\n1:\n" \
@@ -58,4 +70,5 @@ static inline void runtime_const_fixup(void (*fn)(void *, unsigned long),
}
}
+#endif /* __ASSEMBLY__ */
#endif
diff --git a/arch/x86/lib/getuser.S b/arch/x86/lib/getuser.S
index 4357ec2a0bfc..f7589d4142cd 100644
--- a/arch/x86/lib/getuser.S
+++ b/arch/x86/lib/getuser.S
@@ -32,6 +32,7 @@
#include <asm/errno.h>
#include <asm/asm-offsets.h>
#include <asm/thread_info.h>
+#include <asm/runtime-const.h>
#include <asm/asm.h>
#include <asm/smap.h>
@@ -39,11 +40,7 @@
.macro check_range size:req
.if IS_ENABLED(CONFIG_X86_64)
- movq $0x0123456789abcdef,%rdx
- 1:
- .pushsection runtime_ptr_USER_PTR_MAX,"a"
- .long 1b - 8 - .
- .popsection
+ RUNTIME_CONST_PTR sym=USER_PTR_MAX reg=rdx
cmp %rax, %rdx
sbb %rdx, %rdx
or %rdx, %rax
--
Kiryl Shutsemau / Kirill A. Shutemov
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