Re: [PATCH] x86/uaccess: Avoid barrier_nospec() in copy_from_user()
From: Kirill A. Shutemov <hidden>
Date: 2024-10-14 12:30:38
Subsystem:
the rest, x86 architecture (32-bit and 64-bit) · Maintainers:
Linus Torvalds, Thomas Gleixner, Ingo Molnar, Borislav Petkov, Dave Hansen
On Sun, Oct 13, 2024 at 11:50:55PM -0700, Linus Torvalds wrote:
quoted hunk ↗ jump to hunk
Anyway, the attached patchdiff --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