On March 7, 2025 1:20:17 AM PST, Uros Bizjak <ubizjak@xxxxxxxxx> wrote: >On Fri, Mar 7, 2025 at 4:00 AM H. Peter Anvin <hpa@xxxxxxxxx> wrote: >> >> On March 6, 2025 1:33:43 PM PST, tip-bot2 for Uros Bizjak <tip-bot2@xxxxxxxxxxxxx> wrote: >> >The following commit has been merged into the x86/asm branch of tip: >> > >> >Commit-ID: aa3942d4d12ef57f031faa2772fe410c24191e36 >> >Gitweb: https://git.kernel.org/tip/aa3942d4d12ef57f031faa2772fe410c24191e36 >> >Author: Uros Bizjak <ubizjak@xxxxxxxxx> >> >AuthorDate: Thu, 06 Mar 2025 15:52:11 +01:00 >> >Committer: Ingo Molnar <mingo@xxxxxxxxxx> >> >CommitterDate: Thu, 06 Mar 2025 22:04:48 +01:00 >> > >> >x86/kexec: Merge x86_32 and x86_64 code using macros from <asm/asm.h> >> > >> >Merge common x86_32 and x86_64 code in crash_setup_regs() >> >using macros from <asm/asm.h>. >> > >> >The compiled object files before and after the patch are unchanged. >> > >> >Signed-off-by: Uros Bizjak <ubizjak@xxxxxxxxx> >> >Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx> >> >Cc: David Woodhouse <dwmw@xxxxxxxxxxxx> >> >Cc: Baoquan He <bhe@xxxxxxxxxx> >> >Cc: Vivek Goyal <vgoyal@xxxxxxxxxx> >> >Cc: Dave Young <dyoung@xxxxxxxxxx> >> >Cc: Ard Biesheuvel <ardb@xxxxxxxxxx> >> >Cc: "H. Peter Anvin" <hpa@xxxxxxxxx> >> >Link: https://lore.kernel.org/r/20250306145227.55819-1-ubizjak@xxxxxxxxx >> >--- >> > arch/x86/include/asm/kexec.h | 58 +++++++++++++++-------------------- >> > 1 file changed, 25 insertions(+), 33 deletions(-) >> > >> >diff --git a/arch/x86/include/asm/kexec.h b/arch/x86/include/asm/kexec.h >> >index 8ad1874..e3589d6 100644 >> >--- a/arch/x86/include/asm/kexec.h >> >+++ b/arch/x86/include/asm/kexec.h >> >@@ -18,6 +18,7 @@ >> > #include <linux/string.h> >> > #include <linux/kernel.h> >> > >> >+#include <asm/asm.h> >> > #include <asm/page.h> >> > #include <asm/ptrace.h> >> > >> >@@ -71,41 +72,32 @@ static inline void crash_setup_regs(struct pt_regs *newregs, >> > if (oldregs) { >> > memcpy(newregs, oldregs, sizeof(*newregs)); >> > } else { >> >+ asm volatile("mov %%" _ASM_BX ",%0" : "=m"(newregs->bx)); >> >+ asm volatile("mov %%" _ASM_CX ",%0" : "=m"(newregs->cx)); >> >+ asm volatile("mov %%" _ASM_DX ",%0" : "=m"(newregs->dx)); >> >+ asm volatile("mov %%" _ASM_SI ",%0" : "=m"(newregs->si)); >> >+ asm volatile("mov %%" _ASM_DI ",%0" : "=m"(newregs->di)); >> >+ asm volatile("mov %%" _ASM_BP ",%0" : "=m"(newregs->bp)); >> >+ asm volatile("mov %%" _ASM_AX ",%0" : "=m"(newregs->ax)); >> >+ asm volatile("mov %%" _ASM_SP ",%0" : "=m"(newregs->sp)); >> >+#ifdef CONFIG_X86_64 >> >+ asm volatile("mov %%r8,%0" : "=m"(newregs->r8)); >> >+ asm volatile("mov %%r9,%0" : "=m"(newregs->r9)); >> >+ asm volatile("mov %%r10,%0" : "=m"(newregs->r10)); >> >+ asm volatile("mov %%r11,%0" : "=m"(newregs->r11)); >> >+ asm volatile("mov %%r12,%0" : "=m"(newregs->r12)); >> >+ asm volatile("mov %%r13,%0" : "=m"(newregs->r13)); >> >+ asm volatile("mov %%r14,%0" : "=m"(newregs->r14)); >> >+ asm volatile("mov %%r15,%0" : "=m"(newregs->r15)); >> >+#endif >> >+ asm volatile("mov %%ss,%k0" : "=a"(newregs->ss)); >> >+ asm volatile("mov %%cs,%k0" : "=a"(newregs->cs)); >> > #ifdef CONFIG_X86_32 >> >- asm volatile("movl %%ebx,%0" : "=m"(newregs->bx)); >> >- asm volatile("movl %%ecx,%0" : "=m"(newregs->cx)); >> >- asm volatile("movl %%edx,%0" : "=m"(newregs->dx)); >> >- asm volatile("movl %%esi,%0" : "=m"(newregs->si)); >> >- asm volatile("movl %%edi,%0" : "=m"(newregs->di)); >> >- asm volatile("movl %%ebp,%0" : "=m"(newregs->bp)); >> >- asm volatile("movl %%eax,%0" : "=m"(newregs->ax)); >> >- asm volatile("movl %%esp,%0" : "=m"(newregs->sp)); >> >- asm volatile("movl %%ss, %%eax;" :"=a"(newregs->ss)); >> >- asm volatile("movl %%cs, %%eax;" :"=a"(newregs->cs)); >> >- asm volatile("movl %%ds, %%eax;" :"=a"(newregs->ds)); >> >- asm volatile("movl %%es, %%eax;" :"=a"(newregs->es)); >> >- asm volatile("pushfl; popl %0" :"=m"(newregs->flags)); >> >-#else >> >- asm volatile("movq %%rbx,%0" : "=m"(newregs->bx)); >> >- asm volatile("movq %%rcx,%0" : "=m"(newregs->cx)); >> >- asm volatile("movq %%rdx,%0" : "=m"(newregs->dx)); >> >- asm volatile("movq %%rsi,%0" : "=m"(newregs->si)); >> >- asm volatile("movq %%rdi,%0" : "=m"(newregs->di)); >> >- asm volatile("movq %%rbp,%0" : "=m"(newregs->bp)); >> >- asm volatile("movq %%rax,%0" : "=m"(newregs->ax)); >> >- asm volatile("movq %%rsp,%0" : "=m"(newregs->sp)); >> >- asm volatile("movq %%r8,%0" : "=m"(newregs->r8)); >> >- asm volatile("movq %%r9,%0" : "=m"(newregs->r9)); >> >- asm volatile("movq %%r10,%0" : "=m"(newregs->r10)); >> >- asm volatile("movq %%r11,%0" : "=m"(newregs->r11)); >> >- asm volatile("movq %%r12,%0" : "=m"(newregs->r12)); >> >- asm volatile("movq %%r13,%0" : "=m"(newregs->r13)); >> >- asm volatile("movq %%r14,%0" : "=m"(newregs->r14)); >> >- asm volatile("movq %%r15,%0" : "=m"(newregs->r15)); >> >- asm volatile("movl %%ss, %%eax;" :"=a"(newregs->ss)); >> >- asm volatile("movl %%cs, %%eax;" :"=a"(newregs->cs)); >> >- asm volatile("pushfq; popq %0" :"=m"(newregs->flags)); >> >+ asm volatile("mov %%ds,%k0" : "=a"(newregs->ds)); >> >+ asm volatile("mov %%es,%k0" : "=a"(newregs->es)); >> > #endif >> >+ asm volatile("pushf\n\t" >> >+ "pop %0" : "=m"(newregs->flags)); >> > newregs->ip = _THIS_IP_; >> > } >> > } >> >> Incidentally, doing this in C code is obviously completely broken, especially doing it in multiple statements. You have no idea what the compiler has messed with before you get there. > >These are "asm volatile" statemets, so at least they won't be >scheduled in a different way. OTOH, please note that the patch is very >carefully written to not change code flow, usage of hardregs in the >inline asm is usually the sign of fragile code. > >Uros. > That doesn't matter, though; that only means they can't be moved relatively to each other, but the compiler is perfectly capable of inserting code before, or in between. Your patch might be a functional null, but the code is broken on a deep and fundamental basis.
![]() |