From a5f7a5bb3b7f28ba7e4fa246775b29a0e5537255 Mon Sep 17 00:00:00 2001 From: Jinke Han Date: Tue, 8 Sep 2026 15:37:42 +0800 Subject: x86/kprobes: Fix crash when probing CS CALL instructions When using eBPF to probe CS CALL instructions within a function, a crash can be triggered. The eBPF tool probes offset 257 of the __hrtimer_run_queues() function: <__hrtimer_run_queues+249>: nopl 0x0(%rax,%rax,1) <__hrtimer_run_queues+254>: mov %r14,%rdi <__hrtimer_run_queues+257>: cs call <__x86_indirect_thunk_r12> <__hrtimer_run_queues+263>: mov %eax,%r12d <__hrtimer_run_queues+266>: xchg %ax,%ax <__hrtimer_run_queues+268>: mov %r13,%rdi Which triggers this crash: BUG: unable to handle page fault for address: 00000000000f41c9 #PF: supervisor write access in kernel mode #PF: error_code(0x0002) - not-present page PGD 0 P4D 0 Oops: 0002 [#1] SMP NOPTI CPU: 1 PID: 0 Comm: swapper/1 Kdump: loaded Tainted: P RIP: 0010:__hrtimer_run_queues+0x106/0x230 Note that __hrtimer_run_queues+0x106 is __hrtimer_run_queues+262, which is at the 6th byte of the above CS CALL instruction. Since the CS CALL instruction occupies 6 bytes, the exception occurred in the middle of that call instruction. The root cause is that when using eBPF tools to probe in the middle of a function, a kprobe with INT3 is used as the underlying implementation. During single-step emulation of the original CALL instruction, int3_emulate_call() assumes that the probed CALL instruction is 5 bytes long. However, the actual CS-prefixed CALL instruction occupies 6 bytes, so it constructs an incorrect exception return address. When the CPU returns from the kprobe handler, the next instruction to be executed is at the address of the last byte of that CS CALL instruction. Coincidentally, starting from that address, the CPU fetches and decodes a completely different instruction, which ultimately triggers a kernel crash. Fix the issue by using the actual instruction length obtained from the instruction decoder when constructing the exception return address, rather than relying on the hardcoded CALL_INSN_SIZE macro. [ mingo: Refined the changelog ] Fixes: 6256e668b7af ("x86/kprobes: Use int3 instead of debug trap for single-step") Suggested-by: Masami Hiramatsu (Google) Signed-off-by: Jinke Han Signed-off-by: Ingo Molnar Reviewed-by: Masami Hiramatsu (Google) Acked-by: Yafang Shao Acked-by: Borislav Petkov Cc: Peter Zijlstra Link: https://patch.msgid.link/20260908073742.GA10517@didi-ThinkCentre-M920t-N000 --- arch/powerpc/mm/cacheflush.c | 221 +++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 221 insertions(+) create mode 100644 arch/powerpc/mm/cacheflush.c (limited to 'arch/powerpc/mm/cacheflush.c') diff --git a/arch/powerpc/mm/cacheflush.c b/arch/powerpc/mm/cacheflush.c new file mode 100644 index 000000000..7186516ec --- /dev/null +++ b/arch/powerpc/mm/cacheflush.c @@ -0,0 +1,221 @@ +// SPDX-License-Identifier: GPL-2.0-or-later + +#include +#include + +/** + * flush_coherent_icache() - if a CPU has a coherent icache, flush it + * Return true if the cache was flushed, false otherwise + */ +static inline bool flush_coherent_icache(void) +{ + /* + * For a snooping icache, we still need a dummy icbi to purge all the + * prefetched instructions from the ifetch buffers. We also need a sync + * before the icbi to order the actual stores to memory that might + * have modified instructions with the icbi. + */ + if (cpu_has_feature(CPU_FTR_COHERENT_ICACHE)) { + mb(); /* sync */ + icbi((void *)PAGE_OFFSET); + mb(); /* sync */ + isync(); + return true; + } + + return false; +} + +/** + * invalidate_icache_range() - Flush the icache by issuing icbi across an address range + * @start: the start address + * @stop: the stop address (exclusive) + */ +static void invalidate_icache_range(unsigned long start, unsigned long stop) +{ + unsigned long shift = l1_icache_shift(); + unsigned long bytes = l1_icache_bytes(); + char *addr = (char *)(start & ~(bytes - 1)); + unsigned long size = stop - (unsigned long)addr + (bytes - 1); + unsigned long i; + + for (i = 0; i < size >> shift; i++, addr += bytes) + icbi(addr); + + mb(); /* sync */ + isync(); +} + +/** + * flush_icache_range: Write any modified data cache blocks out to memory + * and invalidate the corresponding blocks in the instruction cache + * + * Generic code will call this after writing memory, before executing from it. + * + * @start: the start address + * @stop: the stop address (exclusive) + */ +void flush_icache_range(unsigned long start, unsigned long stop) +{ + if (flush_coherent_icache()) + return; + + clean_dcache_range(start, stop); + + if (IS_ENABLED(CONFIG_44x)) { + /* + * Flash invalidate on 44x because we are passed kmapped + * addresses and this doesn't work for userspace pages due to + * the virtually tagged icache. + */ + iccci((void *)start); + mb(); /* sync */ + isync(); + } else + invalidate_icache_range(start, stop); +} +EXPORT_SYMBOL(flush_icache_range); + +#ifdef CONFIG_HIGHMEM +/** + * flush_dcache_icache_phys() - Flush a page by its physical address + * @physaddr: the physical address of the page + */ +static void flush_dcache_icache_phys(unsigned long physaddr) +{ + unsigned long bytes = l1_dcache_bytes(); + unsigned long nb = PAGE_SIZE / bytes; + unsigned long addr = physaddr & PAGE_MASK; + unsigned long msr, msr0; + unsigned long loop1 = addr, loop2 = addr; + + msr0 = mfmsr(); + msr = msr0 & ~MSR_DR; + /* + * This must remain as ASM to prevent potential memory accesses + * while the data MMU is disabled + */ + asm volatile( + " mtctr %2;\n" + " mtmsr %3;\n" + " isync;\n" + "0: dcbst 0, %0;\n" + " addi %0, %0, %4;\n" + " bdnz 0b;\n" + " sync;\n" + " mtctr %2;\n" + "1: icbi 0, %1;\n" + " addi %1, %1, %4;\n" + " bdnz 1b;\n" + " sync;\n" + " mtmsr %5;\n" + " isync;\n" + : "+&r" (loop1), "+&r" (loop2) + : "r" (nb), "r" (msr), "i" (bytes), "r" (msr0) + : "ctr", "memory"); +} +NOKPROBE_SYMBOL(flush_dcache_icache_phys) +#else +static void flush_dcache_icache_phys(unsigned long physaddr) +{ +} +#endif + +/** + * __flush_dcache_icache(): Flush a particular page from the data cache to RAM. + * Note: this is necessary because the instruction cache does *not* + * snoop from the data cache. + * + * @p: the address of the page to flush + */ +static void __flush_dcache_icache(void *p) +{ + unsigned long addr = (unsigned long)p & PAGE_MASK; + + clean_dcache_range(addr, addr + PAGE_SIZE); + + /* + * We don't flush the icache on 44x. Those have a virtual icache and we + * don't have access to the virtual address here (it's not the page + * vaddr but where it's mapped in user space). The flushing of the + * icache on these is handled elsewhere, when a change in the address + * space occurs, before returning to user space. + */ + + if (mmu_has_feature(MMU_FTR_TYPE_44x)) + return; + + invalidate_icache_range(addr, addr + PAGE_SIZE); +} + +void flush_dcache_icache_folio(struct folio *folio) +{ + unsigned int i, nr = folio_nr_pages(folio); + + if (flush_coherent_icache()) + return; + + if (!folio_test_highmem(folio)) { + void *addr = folio_address(folio); + for (i = 0; i < nr; i++) + __flush_dcache_icache(addr + i * PAGE_SIZE); + } else if (IS_ENABLED(CONFIG_BOOKE) || sizeof(phys_addr_t) > sizeof(void *)) { + for (i = 0; i < nr; i++) { + void *start = kmap_local_folio(folio, i * PAGE_SIZE); + + __flush_dcache_icache(start); + kunmap_local(start); + } + } else { + unsigned long pfn = folio_pfn(folio); + for (i = 0; i < nr; i++) + flush_dcache_icache_phys((pfn + i) * PAGE_SIZE); + } +} +EXPORT_SYMBOL(flush_dcache_icache_folio); + +void clear_user_page(void *page, unsigned long vaddr, struct page *pg) +{ + clear_page(page); + + /* + * We shouldn't have to do this, but some versions of glibc + * require it (ld.so assumes zero filled pages are icache clean) + * - Anton + */ + flush_dcache_page(pg); +} +EXPORT_SYMBOL(clear_user_page); + +void copy_user_page(void *vto, void *vfrom, unsigned long vaddr, + struct page *pg) +{ + copy_page(vto, vfrom); + + /* + * We should be able to use the following optimisation, however + * there are two problems. + * Firstly a bug in some versions of binutils meant PLT sections + * were not marked executable. + * Secondly the first word in the GOT section is blrl, used + * to establish the GOT address. Until recently the GOT was + * not marked executable. + * - Anton + */ +#if 0 + if (!vma->vm_file && ((vma->vm_flags & VM_EXEC) == 0)) + return; +#endif + + flush_dcache_page(pg); +} + +void flush_icache_user_page(struct vm_area_struct *vma, struct page *page, + unsigned long addr, int len) +{ + void *maddr; + + maddr = kmap_local_page(page) + (addr & ~PAGE_MASK); + flush_icache_range((unsigned long)maddr, (unsigned long)maddr + len); + kunmap_local(maddr); +} -- cgit v1.3.1