diff --git a/arch/x86/include/asm/uaccess.h b/arch/x86/include/asm/uaccess.h index 913e593..c462079 100644 --- a/arch/x86/include/asm/uaccess.h +++ b/arch/x86/include/asm/uaccess.h @@ -502,9 +502,6 @@ strncpy_from_user(char *dst, const char __user *src, long count); extern __must_check long strnlen_user(const char __user *str, long n); -unsigned long __must_check clear_user(void __user *mem, unsigned long len); -unsigned long __must_check __clear_user(void __user *mem, unsigned long len); - #ifdef CONFIG_ARCH_HAS_COPY_MC unsigned long __must_check copy_mc_to_kernel(void *to, const void *from, unsigned len); @@ -526,6 +523,8 @@ extern struct movsl_mask { #define ARCH_HAS_NOCACHE_UACCESS 1 #ifdef CONFIG_X86_32 +unsigned long __must_check clear_user(void __user *mem, unsigned long len); +unsigned long __must_check __clear_user(void __user *mem, unsigned long len); # include #else # include diff --git a/arch/x86/include/asm/uaccess_64.h b/arch/x86/include/asm/uaccess_64.h index 45697e0..d13d71a 100644 --- a/arch/x86/include/asm/uaccess_64.h +++ b/arch/x86/include/asm/uaccess_64.h @@ -79,4 +79,49 @@ __copy_from_user_flushcache(void *dst, const void __user *src, unsigned size) kasan_check_write(dst, size); return __copy_user_flushcache(dst, src, size); } + +/* + * Zero Userspace. + */ + +__must_check unsigned long +clear_user_original(void __user *addr, unsigned long len); +__must_check unsigned long +clear_user_rep_good(void __user *addr, unsigned long len); +__must_check unsigned long +clear_user_erms(void __user *addr, unsigned long len); + +static __always_inline __must_check unsigned long __clear_user(void __user *addr, unsigned long size) +{ + might_fault(); + stac(); + + /* + * No memory constraint because it doesn't change any memory gcc + * knows about. + */ + asm volatile( + "1:\n\t" + ALTERNATIVE_3("rep stosb", + "call clear_user_erms", ALT_NOT(X86_FEATURE_FSRM), + "call clear_user_rep_good", ALT_NOT(X86_FEATURE_ERMS), + "call clear_user_original", ALT_NOT(X86_FEATURE_REP_GOOD)) + "2:\n" + _ASM_EXTABLE_UA(1b, 2b) + : "+c" (size), "+D" (addr), ASM_CALL_CONSTRAINT + : "a" (0) + /* rep_good clobbers %rdx */ + : "rdx"); + + clac(); + + return size; +} + +static __always_inline unsigned long clear_user(void __user *to, unsigned long n) +{ + if (access_ok(to, n)) + return __clear_user(to, n); + return n; +} #endif /* _ASM_X86_UACCESS_64_H */ diff --git a/arch/x86/lib/clear_page_64.S b/arch/x86/lib/clear_page_64.S index fe59b8a..ecbfb4d 100644 --- a/arch/x86/lib/clear_page_64.S +++ b/arch/x86/lib/clear_page_64.S @@ -1,5 +1,6 @@ /* SPDX-License-Identifier: GPL-2.0-only */ #include +#include #include /* @@ -50,3 +51,140 @@ SYM_FUNC_START(clear_page_erms) RET SYM_FUNC_END(clear_page_erms) EXPORT_SYMBOL_GPL(clear_page_erms) + +/* + * Default clear user-space. + * Input: + * rdi destination + * rcx count + * + * Output: + * rcx: uncleared bytes or 0 if successful. + */ +SYM_FUNC_START(clear_user_original) + /* + * Copy only the lower 32 bits of size as that is enough to handle the rest bytes, + * i.e., no need for a 'q' suffix and thus a REX prefix. + */ + mov %ecx,%eax + shr $3,%rcx + jz .Lrest_bytes + + # do the qwords first + .p2align 4 +.Lqwords: + movq $0,(%rdi) + lea 8(%rdi),%rdi + dec %rcx + jnz .Lqwords + +.Lrest_bytes: + and $7, %eax + jz .Lexit + + # now do the rest bytes +.Lbytes: + movb $0,(%rdi) + inc %rdi + dec %eax + jnz .Lbytes + +.Lexit: + /* + * %rax still needs to be cleared in the exception case because this function is called + * from inline asm and the compiler expects %rax to be zero when exiting the inline asm, + * in case it might reuse it somewhere. + */ + xor %eax,%eax + RET + +.Lqwords_exception: + # convert remaining qwords back into bytes to return to caller + shl $3, %rcx + and $7, %eax + add %rax,%rcx + jmp .Lexit + +.Lbytes_exception: + mov %eax,%ecx + jmp .Lexit + + _ASM_EXTABLE_UA(.Lqwords, .Lqwords_exception) + _ASM_EXTABLE_UA(.Lbytes, .Lbytes_exception) +SYM_FUNC_END(clear_user_original) +EXPORT_SYMBOL(clear_user_original) + +/* + * Alternative clear user-space when CPU feature X86_FEATURE_REP_GOOD is + * present. + * Input: + * rdi destination + * rcx count + * + * Output: + * rcx: uncleared bytes or 0 if successful. + */ +SYM_FUNC_START(clear_user_rep_good) + # call the original thing for less than a cacheline + cmp $64, %rcx + jb clear_user_original + +.Lprep: + # copy lower 32-bits for rest bytes + mov %ecx, %edx + shr $3, %rcx + jz .Lrep_good_rest_bytes + +.Lrep_good_qwords: + rep stosq + +.Lrep_good_rest_bytes: + and $7, %edx + jz .Lrep_good_exit + +.Lrep_good_bytes: + mov %edx, %ecx + rep stosb + +.Lrep_good_exit: + # see .Lexit comment above + xor %eax, %eax + RET + +.Lrep_good_qwords_exception: + # convert remaining qwords back into bytes to return to caller + shl $3, %rcx + and $7, %edx + add %rdx, %rcx + jmp .Lrep_good_exit + + _ASM_EXTABLE_UA(.Lrep_good_qwords, .Lrep_good_qwords_exception) + _ASM_EXTABLE_UA(.Lrep_good_bytes, .Lrep_good_exit) +SYM_FUNC_END(clear_user_rep_good) +EXPORT_SYMBOL(clear_user_rep_good) + +/* + * Alternative clear user-space when CPU feature X86_FEATURE_ERMS is present. + * Input: + * rdi destination + * rcx count + * + * Output: + * rcx: uncleared bytes or 0 if successful. + * + */ +SYM_FUNC_START(clear_user_erms) + # call the original thing for less than a cacheline + cmp $64, %rcx + jb clear_user_original + +.Lerms_bytes: + rep stosb + +.Lerms_exit: + xorl %eax,%eax + RET + + _ASM_EXTABLE_UA(.Lerms_bytes, .Lerms_exit) +SYM_FUNC_END(clear_user_erms) +EXPORT_SYMBOL(clear_user_erms) diff --git a/arch/x86/lib/usercopy_64.c b/arch/x86/lib/usercopy_64.c index 0ae6cf8..6c1f8ac 100644 --- a/arch/x86/lib/usercopy_64.c +++ b/arch/x86/lib/usercopy_64.c @@ -14,46 +14,6 @@ * Zero Userspace */ -unsigned long __clear_user(void __user *addr, unsigned long size) -{ - long __d0; - might_fault(); - /* no memory constraint because it doesn't change any memory gcc knows - about */ - stac(); - asm volatile( - " testq %[size8],%[size8]\n" - " jz 4f\n" - " .align 16\n" - "0: movq $0,(%[dst])\n" - " addq $8,%[dst]\n" - " decl %%ecx ; jnz 0b\n" - "4: movq %[size1],%%rcx\n" - " testl %%ecx,%%ecx\n" - " jz 2f\n" - "1: movb $0,(%[dst])\n" - " incq %[dst]\n" - " decl %%ecx ; jnz 1b\n" - "2:\n" - - _ASM_EXTABLE_TYPE_REG(0b, 2b, EX_TYPE_UCOPY_LEN8, %[size1]) - _ASM_EXTABLE_UA(1b, 2b) - - : [size8] "=&c"(size), [dst] "=&D" (__d0) - : [size1] "r"(size & 7), "[size8]" (size / 8), "[dst]"(addr)); - clac(); - return size; -} -EXPORT_SYMBOL(__clear_user); - -unsigned long clear_user(void __user *to, unsigned long n) -{ - if (access_ok(to, n)) - return __clear_user(to, n); - return n; -} -EXPORT_SYMBOL(clear_user); - #ifdef CONFIG_ARCH_HAS_UACCESS_FLUSHCACHE /** * clean_cache_range - write back a cache range with CLWB diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c index fa71a5d..a498ae1 100644 --- a/arch/x86/mm/fault.c +++ b/arch/x86/mm/fault.c @@ -769,6 +769,8 @@ show_signal_msg(struct pt_regs *regs, unsigned long error_code, unsigned long address, struct task_struct *tsk) { const char *loglvl = task_pid_nr(tsk) > 1 ? KERN_INFO : KERN_EMERG; + /* This is a racy snapshot, but it's better than nothing. */ + int cpu = raw_smp_processor_id(); if (!unhandled_signal(tsk, SIGSEGV)) return; @@ -782,6 +784,14 @@ show_signal_msg(struct pt_regs *regs, unsigned long error_code, print_vma_addr(KERN_CONT " in ", regs->ip); + /* + * Dump the likely CPU where the fatal segfault happened. + * This can help identify faulty hardware. + */ + printk(KERN_CONT " likely on CPU %d (core %d, socket %d)", cpu, + topology_core_id(cpu), topology_physical_package_id(cpu)); + + printk(KERN_CONT "\n"); show_opcodes(regs, loglvl); diff --git a/tools/objtool/check.c b/tools/objtool/check.c index 48e1873..4a9ba6a 100644 --- a/tools/objtool/check.c +++ b/tools/objtool/check.c @@ -1073,6 +1073,9 @@ static const char *uaccess_safe_builtin[] = { "copy_mc_fragile_handle_tail", "copy_mc_enhanced_fast_string", "ftrace_likely_update", /* CONFIG_TRACE_BRANCH_PROFILING */ + "clear_user_erms", + "clear_user_rep_good", + "clear_user_original", NULL };