On Thu, Jun 26, 2025 at 11:35:21AM +0200, Vegard Nossum wrote: > > On 26/06/2025 11:22, Vegard Nossum wrote: > > > > On 25/06/2025 14:50, Kirill A. Shutemov wrote: > > > Linear Address Space Separation (LASS) is a security feature that > > > intends to > > > prevent malicious virtual address space accesses across user/kernel mode. > > > > I applied these patches on top of tip/master and when I try to boot it > > fails with errno 12 (ENOMEM - Cannot allocate memory): > > > > [ 1.517526] Kernel panic - not syncing: Requested init /bin/bash > > failed (error -12). For some reason, I failed to reproduce it. What is your toolchain? > > Just using standard defconfig and booting in qemu/KVM with 2G RAM. > > > > Bisect lands on "x86/asm: Introduce inline memcpy and memset". > > I think the newly added mulq to rep_stos_alternative clobbers %rdx, Yes, it makes sense. > at > least this patch fixed it for me: > > diff --git a/arch/x86/include/asm/string.h b/arch/x86/include/asm/string.h > index 5cd0f18a431fe..bc096526432a1 100644 > --- a/arch/x86/include/asm/string.h > +++ b/arch/x86/include/asm/string.h > @@ -28,7 +28,7 @@ static __always_inline void *__inline_memcpy(void *to, > const void *from, size_t > "2:\n\t" > _ASM_EXTABLE_UA(1b, 2b) > :"+c" (len), "+D" (to), "+S" (from), > ASM_CALL_CONSTRAINT > - : : "memory", _ASM_AX); > + : : "memory", _ASM_AX, _ASM_DX); > > return ret + len; > } This part is not needed. rep_movs_alternative() doesn't touch RDX. I will fold the patch below. Or maybe some asm guru can suggest a better way to fix it without clobbering RDX? diff --git a/arch/x86/include/asm/string.h b/arch/x86/include/asm/string.h index 5cd0f18a431f..b0a26a3f11e0 100644 --- a/arch/x86/include/asm/string.h +++ b/arch/x86/include/asm/string.h @@ -44,7 +44,7 @@ static __always_inline void *__inline_memset(void *addr, int v, size_t len) _ASM_EXTABLE_UA(1b, 2b) : "+c" (len), "+D" (addr), ASM_CALL_CONSTRAINT : "a" ((uint8_t)v) - : "memory", _ASM_SI); + : "memory", _ASM_SI, _ASM_DX); return ret + len; } diff --git a/arch/x86/lib/clear_page_64.S b/arch/x86/lib/clear_page_64.S index ca94828def62..d904c781fa3f 100644 --- a/arch/x86/lib/clear_page_64.S +++ b/arch/x86/lib/clear_page_64.S @@ -64,12 +64,15 @@ EXPORT_SYMBOL_GPL(clear_page_erms) * * Output: * rcx: uncleared bytes or 0 if successful. + * rdx: clobbered */ SYM_FUNC_START(rep_stos_alternative) ANNOTATE_NOENDBR movzbq %al, %rsi movabs $0x0101010101010101, %rax + + /* %rdx:%rax = %rax * %rsi */ mulq %rsi cmpq $64,%rcx -- Kiryl Shutsemau / Kirill A. Shutemov
