powerpc/mm: Warn if W+X pages found on boot (453d87f6) · Commits · 戴 / test

arch/powerpc/Kconfig.debug

+19 −0

Original line number	Diff line number	Diff line
		@@ -361,6 +361,25 @@ config PPC_PTDUMP

		If you are unsure, say N.

		config PPC_DEBUG_WX
		bool "Warn on W+X mappings at boot"
		depends on PPC_PTDUMP
		help
		Generate a warning if any W+X mappings are found at boot.

		This is useful for discovering cases where the kernel is leaving
		W+X mappings after applying NX, as such mappings are a security risk.

		Note that even if the check fails, your kernel is possibly
		still fine, as W+X mappings are not a security hole in
		themselves, what they do is that they make the exploitation
		of other unfixed kernel bugs easier.

		There is no runtime or memory usage effect of this option
		once the kernel has booted up - it's a one time check.

		If in doubt, say "Y".

		config PPC_FAST_ENDIAN_SWITCH
		bool "Deprecated fast endian-switch syscall"
		depends on DEBUG_KERNEL && PPC_BOOK3S_64

arch/powerpc/include/asm/pgtable.h

+6 −0

Original line number	Diff line number	Diff line
		@@ -105,6 +105,12 @@ void mark_initmem_nx(void);
		static inline void mark_initmem_nx(void) { }
		#endif

		#ifdef CONFIG_PPC_DEBUG_WX
		void ptdump_check_wx(void);
		#else
		static inline void ptdump_check_wx(void) { }
		#endif

		/*
		* When used, PTE_FRAG_NR is defined in subarch pgtable.h
		* so we are sure it is included when arriving here.

arch/powerpc/mm/pgtable_32.c

+3 −0

Original line number	Diff line number	Diff line
		@@ -396,6 +396,9 @@ void mark_rodata_ro(void)
		PFN_DOWN((unsigned long)__start_rodata);

		change_page_attr(page, numpages, PAGE_KERNEL_RO);

		// mark_initmem_nx() should have already run by now
		ptdump_check_wx();
		}
		#endif

arch/powerpc/mm/pgtable_64.c

+3 −0

Original line number	Diff line number	Diff line
		@@ -332,6 +332,9 @@ void mark_rodata_ro(void)
		radix__mark_rodata_ro();
		else
		hash__mark_rodata_ro();

		// mark_initmem_nx() should have already run by now
		ptdump_check_wx();
		}

		void mark_initmem_nx(void)

arch/powerpc/mm/ptdump/ptdump.c

+42 −1

Original line number	Diff line number	Diff line
		@@ -31,7 +31,7 @@
		#include "ptdump.h"

		#ifdef CONFIG_PPC32
		#define KERN_VIRT_START 0
		#define KERN_VIRT_START PAGE_OFFSET
		#endif

		/*
		@@ -68,6 +68,8 @@ struct pg_state {
		unsigned long last_pa;
		unsigned int level;
		u64 current_flags;
		bool check_wx;
		unsigned long wx_pages;
		};

		struct addr_marker {
		@@ -181,6 +183,20 @@ static void dump_addr(struct pg_state *st, unsigned long addr)

		}

		static void note_prot_wx(struct pg_state *st, unsigned long addr)
		{
		if (!st->check_wx)
		return;

		if (!((st->current_flags & pgprot_val(PAGE_KERNEL_X)) == pgprot_val(PAGE_KERNEL_X)))
		return;

		WARN_ONCE(1, "powerpc/mm: Found insecure W+X mapping at address %p/%pS\n",
		(void )st->start_address, (void )st->start_address);

		st->wx_pages += (addr - st->start_address) / PAGE_SIZE;
		}

		static void note_page(struct pg_state *st, unsigned long addr,
		unsigned int level, u64 val)
		{
		@@ -210,6 +226,7 @@ static void note_page(struct pg_state *st, unsigned long addr,

		/* Check the PTE flags */
		if (st->current_flags) {
		note_prot_wx(st, addr);
		dump_addr(st, addr);

		/* Dump all the flags */
		@@ -387,6 +404,30 @@ static void build_pgtable_complete_mask(void)
		pg_level[i].mask \|= pg_level[i].flag[j].mask;
		}

		#ifdef CONFIG_PPC_DEBUG_WX
		void ptdump_check_wx(void)
		{
		struct pg_state st = {
		.seq = NULL,
		.marker = address_markers,
		.check_wx = true,
		};

		if (radix_enabled())
		st.start_address = PAGE_OFFSET;
		else
		st.start_address = KERN_VIRT_START;

		walk_pagetables(&st);

		if (st.wx_pages)
		pr_warn("Checked W+X mappings: FAILED, %lu W+X pages found\n",
		st.wx_pages);
		else
		pr_info("Checked W+X mappings: passed, no W+X pages found\n");
		}
		#endif

		static int ptdump_init(void)
		{
		struct dentry *debugfs_file;

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