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When building with CONFIG_CFI=y and CONFIG_LTO_CLANG_FULL=y, there is a series
of errors from the various versions of clear_page() not having __kcfi_typeid_
symbols.
$ cat kernel/configs/repro.config
CONFIG_CFI=y
# CONFIG_LTO_NONE is not set
CONFIG_LTO_CLANG_FULL=y
$ make -skj"$(nproc)" ARCH=x86_64 LLVM=1 clean defconfig repro.config bzImage
ld.lld: error: undefined symbol: __kcfi_typeid_clear_page_rep
>>> referenced by ld-temp.o
>>> vmlinux.o:(__cfi_clear_page_rep)
ld.lld: error: undefined symbol: __kcfi_typeid_clear_page_orig
>>> referenced by ld-temp.o
>>> vmlinux.o:(__cfi_clear_page_orig)
ld.lld: error: undefined symbol: __kcfi_typeid_clear_page_erms
>>> referenced by ld-temp.o
>>> vmlinux.o:(__cfi_clear_page_erms)
With full LTO, it is possible for LLVM to realize that these functions never
have their address taken (as they are only used within an alternative, which
will make them a direct call) across the whole kernel and either drop or skip
generating their kCFI type identification symbols.
clear_page_{rep,orig,erms}() are defined in clear_page_64.S with
SYM_TYPED_FUNC_START as a result of
2981557cb0 ("x86,kcfi: Fix EXPORT_SYMBOL vs kCFI"),
as exported functions are free to be called indirectly thus need kCFI type
identifiers.
Use KCFI_REFERENCE with these clear_page() functions to force LLVM to see
these functions as address-taken and generate then keep the kCFI type
identifiers.
Fixes: 2981557cb0 ("x86,kcfi: Fix EXPORT_SYMBOL vs kCFI")
Closes: https://github.com/ClangBuiltLinux/linux/issues/2128
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Reviewed-by: Sami Tolvanen <samitolvanen@google.com>
Link: https://patch.msgid.link/20251013-x86-fix-clear_page-cfi-full-lto-errors-v1-1-d69534c0be61@kernel.org
106 lines
3.0 KiB
C
106 lines
3.0 KiB
C
/* SPDX-License-Identifier: GPL-2.0 */
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#ifndef _ASM_X86_PAGE_64_H
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#define _ASM_X86_PAGE_64_H
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#include <asm/page_64_types.h>
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#ifndef __ASSEMBLER__
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#include <asm/cpufeatures.h>
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#include <asm/alternative.h>
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#include <linux/kmsan-checks.h>
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/* duplicated to the one in bootmem.h */
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extern unsigned long max_pfn;
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extern unsigned long phys_base;
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extern unsigned long page_offset_base;
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extern unsigned long vmalloc_base;
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extern unsigned long vmemmap_base;
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extern unsigned long direct_map_physmem_end;
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static __always_inline unsigned long __phys_addr_nodebug(unsigned long x)
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{
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unsigned long y = x - __START_KERNEL_map;
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/* use the carry flag to determine if x was < __START_KERNEL_map */
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x = y + ((x > y) ? phys_base : (__START_KERNEL_map - PAGE_OFFSET));
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return x;
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}
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#ifdef CONFIG_DEBUG_VIRTUAL
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extern unsigned long __phys_addr(unsigned long);
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extern unsigned long __phys_addr_symbol(unsigned long);
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#else
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#define __phys_addr(x) __phys_addr_nodebug(x)
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#define __phys_addr_symbol(x) \
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((unsigned long)(x) - __START_KERNEL_map + phys_base)
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#endif
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#define __phys_reloc_hide(x) (x)
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void clear_page_orig(void *page);
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void clear_page_rep(void *page);
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void clear_page_erms(void *page);
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KCFI_REFERENCE(clear_page_orig);
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KCFI_REFERENCE(clear_page_rep);
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KCFI_REFERENCE(clear_page_erms);
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static inline void clear_page(void *page)
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{
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/*
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* Clean up KMSAN metadata for the page being cleared. The assembly call
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* below clobbers @page, so we perform unpoisoning before it.
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*/
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kmsan_unpoison_memory(page, PAGE_SIZE);
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alternative_call_2(clear_page_orig,
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clear_page_rep, X86_FEATURE_REP_GOOD,
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clear_page_erms, X86_FEATURE_ERMS,
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"=D" (page),
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"D" (page),
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"cc", "memory", "rax", "rcx");
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}
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void copy_page(void *to, void *from);
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KCFI_REFERENCE(copy_page);
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/*
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* User space process size. This is the first address outside the user range.
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* There are a few constraints that determine this:
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*
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* On Intel CPUs, if a SYSCALL instruction is at the highest canonical
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* address, then that syscall will enter the kernel with a
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* non-canonical return address, and SYSRET will explode dangerously.
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* We avoid this particular problem by preventing anything
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* from being mapped at the maximum canonical address.
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*
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* On AMD CPUs in the Ryzen family, there's a nasty bug in which the
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* CPUs malfunction if they execute code from the highest canonical page.
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* They'll speculate right off the end of the canonical space, and
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* bad things happen. This is worked around in the same way as the
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* Intel problem.
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*
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* With page table isolation enabled, we map the LDT in ... [stay tuned]
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*/
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static __always_inline unsigned long task_size_max(void)
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{
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unsigned long ret;
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alternative_io("movq %[small],%0","movq %[large],%0",
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X86_FEATURE_LA57,
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"=r" (ret),
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[small] "i" ((1ul << 47)-PAGE_SIZE),
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[large] "i" ((1ul << 56)-PAGE_SIZE));
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return ret;
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}
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#endif /* !__ASSEMBLER__ */
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#ifdef CONFIG_X86_VSYSCALL_EMULATION
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# define __HAVE_ARCH_GATE_AREA 1
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#endif
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#endif /* _ASM_X86_PAGE_64_H */
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