powerpc: Avoid code patching freed init sections (51c3c62b) · Commits · 戴 / test

This stops us from doing code patching in init sections after they've been freed. In this chain: kvm_guest_init() -> kvm_use_magic_page() -> fault_in_pages_readable() -> __get_user() -> __get_user_nocheck() -> barrier_nospec(); We have a code patching location at barrier_nospec() and kvm_guest_init() is an init function. This whole chain gets inlined, so when we free the init section (hence kvm_guest_init()), this code goes away and hence should no longer be patched. We seen this as userspace memory corruption when using a memory checker while doing partition migration testing on powervm (this starts the code patching post migration via /sys/kernel/mobility/migration). In theory, it could also happen when using /sys/kernel/debug/powerpc/barrier_nospec. Cc: stable@vger.kernel.org # 4.13+ Signed-off-by:

Michael Neuling <mikey@neuling.org> Reviewed-by:

Nicholas Piggin <npiggin@gmail.com> Reviewed-by:

Christophe Leroy <christophe.leroy@c-s.fr> Signed-off-by:

Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/include/asm/setup.h

+1 −0

Original line number	Diff line number	Diff line
		@@ -9,6 +9,7 @@ extern void ppc_printk_progress(char *s, unsigned short hex);

		extern unsigned int rtas_data;
		extern unsigned long long memory_limit;
		extern bool init_mem_is_free;
		extern unsigned long klimit;
		extern void *zalloc_maybe_bootmem(size_t size, gfp_t mask);

arch/powerpc/lib/code-patching.c

+6 −0

Original line number	Diff line number	Diff line
		@@ -28,6 +28,12 @@ static int __patch_instruction(unsigned int *exec_addr, unsigned int instr,
		{
		int err;

		/* Make sure we aren't patching a freed init section */
		if (init_mem_is_free && init_section_contains(exec_addr, 4)) {
		pr_debug("Skipping init section patching addr: 0x%px\n", exec_addr);
		return 0;
		}

		__put_user_size(instr, patch_addr, 4, err);
		if (err)
		return err;

arch/powerpc/mm/mem.c

+2 −0

Original line number	Diff line number	Diff line
		@@ -63,6 +63,7 @@
		#endif

		unsigned long long memory_limit;
		bool init_mem_is_free;

		#ifdef CONFIG_HIGHMEM
		pte_t *kmap_pte;
		@@ -396,6 +397,7 @@ void free_initmem(void)
		{
		ppc_md.progress = ppc_printk_progress;
		mark_initmem_nx();
		init_mem_is_free = true;
		free_initmem_default(POISON_FREE_INITMEM);
		}

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