On Sun, Oct 13, 2024 at 11:50:55PM -0700, Linus Torvalds wrote:
> Anyway, the attached patch
>
> diff --git a/arch/x86/lib/getuser.S b/arch/x86/lib/getuser.S
> index d066aecf8aeb..7d5730aa18b8 100644
> --- a/arch/x86/lib/getuser.S
> +++ b/arch/x86/lib/getuser.S
> @@ -37,11 +37,17 @@
>
> #define ASM_BARRIER_NOSPEC ALTERNATIVE "", "lfence", X86_FEATURE_LFENCE_RDTSC
>
> +#define X86_CANONICAL_MASK ALTERNATIVE \
> + "movq $0x80007fffffffffff,%rdx", \
> + "movq $0x80ffffffffffffff,%rdx", X86_FEATURE_LA57
> +
> .macro check_range size:req
> .if IS_ENABLED(CONFIG_X86_64)
> mov %rax, %rdx
> sar $63, %rdx
> or %rdx, %rax
> + X86_CANONICAL_MASK
> + and %rdx,%rax
> .else
> cmp $TASK_SIZE_MAX-\size+1, %eax
> jae .Lbad_get_user
Given that LAM enforces bit 47/56 to be equal to bit 63 I think we can do
this unconditionally instead of masking:
diff --git a/arch/x86/lib/getuser.S b/arch/x86/lib/getuser.S
index d066aecf8aeb..86d4511520b1 100644
--- a/arch/x86/lib/getuser.S
+++ b/arch/x86/lib/getuser.S
@@ -37,9 +37,14 @@
#define ASM_BARRIER_NOSPEC ALTERNATIVE "", "lfence", X86_FEATURE_LFENCE_RDTSC
+#define SHIFT_LEFT_TO_MSB ALTERNATIVE \
+ "shl $(64 - 48), %rdx", \
+ "shl $(64 - 57), %rdx", X86_FEATURE_LA57
+
.macro check_range size:req
.if IS_ENABLED(CONFIG_X86_64)
mov %rax, %rdx
+ SHIFT_LEFT_TO_MSB
sar $63, %rdx
or %rdx, %rax
.else
--
Kiryl Shutsemau / Kirill A. Shutemov
