| Message ID | 1476828091-17802-5-git-send-email-labbott@redhat.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On 18 October 2016 at 23:01, Laura Abbott <labbott@redhat.com> wrote: > > Page mappings with full RWX permissions are a security risk. x86 > has an option to walk the page tables and dump any bad pages. > (See e1a58320a38d ("x86/mm: Warn on W^X mappings")). Add a similar > implementation for arm64. > > Reviewed-by: Kees Cook <keescook@chromium.org> > Reviewed-by: Mark Rutland <mark.rutland@arm.com> > Tested-by: Mark Rutland <mark.rutland@arm.com> > Signed-off-by: Laura Abbott <labbott@redhat.com> > --- > v3: Rebased for header guard fixup, whitespace fixes > --- > arch/arm64/Kconfig.debug | 29 +++++++++++++++++++++++ > arch/arm64/include/asm/ptdump.h | 8 +++++++ > arch/arm64/mm/dump.c | 52 +++++++++++++++++++++++++++++++++++++++++ > arch/arm64/mm/mmu.c | 2 ++ > 4 files changed, 91 insertions(+) > > diff --git a/arch/arm64/Kconfig.debug b/arch/arm64/Kconfig.debug > index 21a5b74..d1ebd46 100644 > --- a/arch/arm64/Kconfig.debug > +++ b/arch/arm64/Kconfig.debug > @@ -42,6 +42,35 @@ config ARM64_RANDOMIZE_TEXT_OFFSET > of TEXT_OFFSET and platforms must not require a specific > value. > > +config DEBUG_WX > + bool "Warn on W+X mappings at boot" > + select ARM64_PTDUMP_CORE > + ---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. > + This check also includes UXN, which should be set on all kernel > + mappings. > + > + Look for a message in dmesg output like this: > + > + arm64/mm: Checked W+X mappings: passed, no W+X pages found. > + > + or like this, if the check failed: > + > + arm64/mm: Checked W+X mappings: FAILED, <N> W+X pages found. > + > + 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 DEBUG_SET_MODULE_RONX > bool "Set loadable kernel module data as NX and text as RO" > depends on MODULES > diff --git a/arch/arm64/include/asm/ptdump.h b/arch/arm64/include/asm/ptdump.h > index f72ee69..6afd847 100644 > --- a/arch/arm64/include/asm/ptdump.h > +++ b/arch/arm64/include/asm/ptdump.h > @@ -42,5 +42,13 @@ static inline int ptdump_debugfs_register(struct ptdump_info *info, > return 0; > } > #endif > +void ptdump_check_wx(void); > #endif /* CONFIG_ARM64_PTDUMP_CORE */ > + > +#ifdef CONFIG_DEBUG_WX > +#define debug_checkwx() ptdump_check_wx() > +#else > +#define debug_checkwx() do { } while (0) > +#endif > + > #endif /* __ASM_PTDUMP_H */ > diff --git a/arch/arm64/mm/dump.c b/arch/arm64/mm/dump.c > index bb36649..4913af5 100644 > --- a/arch/arm64/mm/dump.c > +++ b/arch/arm64/mm/dump.c > @@ -74,6 +74,8 @@ struct pg_state { > unsigned long start_address; > unsigned level; > u64 current_prot; > + bool check_wx; > + unsigned long wx_pages; > }; > > struct prot_bits { > @@ -202,6 +204,35 @@ static void dump_prot(struct pg_state *st, const struct prot_bits *bits, > } > } > > +static void note_prot_uxn(struct pg_state *st, unsigned long addr) > +{ > + if (!st->check_wx) > + return; > + > + if ((st->current_prot & PTE_UXN) == PTE_UXN) > + return; > + > + WARN_ONCE(1, "arm64/mm: Found non-UXN 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_prot_wx(struct pg_state *st, unsigned long addr) > +{ > + if (!st->check_wx) > + return; > + if ((st->current_prot & PTE_RDONLY) == PTE_RDONLY) > + return; > + if ((st->current_prot & PTE_PXN) == PTE_PXN) > + return; > + > + WARN_ONCE(1, "arm64/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; > +} > + Why are these separate functions, and why is wx_pages increased twice, potentially? Given how rare non-UXN kernel mappings should be, could we not just add if ((st->current_prot & PTE_UXN) == 0) WARN(xxx) (without the _ONCE) to note_prot_wx(), and drop note_prot_uxn() entirely? > static void note_page(struct pg_state *st, unsigned long addr, unsigned level, > u64 val) > { > @@ -219,6 +250,8 @@ static void note_page(struct pg_state *st, unsigned long addr, unsigned level, > unsigned long delta; > > if (st->current_prot) { > + note_prot_uxn(st, addr); > + note_prot_wx(st, addr); > pt_dump_seq_printf(st->seq, "0x%016lx-0x%016lx ", > st->start_address, addr); > > @@ -344,6 +377,25 @@ static struct ptdump_info kernel_ptdump_info = { > .base_addr = VA_START, > }; > > +void ptdump_check_wx(void) > +{ > + struct pg_state st = { > + .seq = NULL, > + .marker = (struct addr_marker[]) { > + { -1, NULL}, > + }, > + .check_wx = true, > + }; > + > + walk_pgd(&st, &init_mm, 0); > + note_page(&st, 0, 0, 0); > + if (st.wx_pages) > + pr_info("Checked W+X mappings: FAILED, %lu W+X pages found\n", > + st.wx_pages); Could we upgrade this to pr_warn? > + else > + pr_info("Checked W+X mappings: passed, no W+X pages found\n"); > +} > + > static int ptdump_init(void) > { > ptdump_initialize(); > diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c > index 05615a3..2cbe2fe 100644 > --- a/arch/arm64/mm/mmu.c > +++ b/arch/arm64/mm/mmu.c > @@ -42,6 +42,7 @@ > #include <asm/tlb.h> > #include <asm/memblock.h> > #include <asm/mmu_context.h> > +#include <asm/ptdump.h> > > u64 idmap_t0sz = TCR_T0SZ(VA_BITS); > > @@ -396,6 +397,7 @@ void mark_rodata_ro(void) > section_size = (unsigned long)__init_begin - (unsigned long)__start_rodata; > create_mapping_late(__pa(__start_rodata), (unsigned long)__start_rodata, > section_size, PAGE_KERNEL_RO); > + debug_checkwx(); > } > > static void __init map_kernel_segment(pgd_t *pgd, void *va_start, void *va_end, > -- > 2.7.4 >
On 10/20/2016 03:32 AM, Ard Biesheuvel wrote: > On 18 October 2016 at 23:01, Laura Abbott <labbott@redhat.com> wrote: >> >> Page mappings with full RWX permissions are a security risk. x86 >> has an option to walk the page tables and dump any bad pages. >> (See e1a58320a38d ("x86/mm: Warn on W^X mappings")). Add a similar >> implementation for arm64. >> >> Reviewed-by: Kees Cook <keescook@chromium.org> >> Reviewed-by: Mark Rutland <mark.rutland@arm.com> >> Tested-by: Mark Rutland <mark.rutland@arm.com> >> Signed-off-by: Laura Abbott <labbott@redhat.com> >> --- >> v3: Rebased for header guard fixup, whitespace fixes >> --- >> arch/arm64/Kconfig.debug | 29 +++++++++++++++++++++++ >> arch/arm64/include/asm/ptdump.h | 8 +++++++ >> arch/arm64/mm/dump.c | 52 +++++++++++++++++++++++++++++++++++++++++ >> arch/arm64/mm/mmu.c | 2 ++ >> 4 files changed, 91 insertions(+) >> >> diff --git a/arch/arm64/Kconfig.debug b/arch/arm64/Kconfig.debug >> index 21a5b74..d1ebd46 100644 >> --- a/arch/arm64/Kconfig.debug >> +++ b/arch/arm64/Kconfig.debug >> @@ -42,6 +42,35 @@ config ARM64_RANDOMIZE_TEXT_OFFSET >> of TEXT_OFFSET and platforms must not require a specific >> value. >> >> +config DEBUG_WX >> + bool "Warn on W+X mappings at boot" >> + select ARM64_PTDUMP_CORE >> + ---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. >> + This check also includes UXN, which should be set on all kernel >> + mappings. >> + >> + Look for a message in dmesg output like this: >> + >> + arm64/mm: Checked W+X mappings: passed, no W+X pages found. >> + >> + or like this, if the check failed: >> + >> + arm64/mm: Checked W+X mappings: FAILED, <N> W+X pages found. >> + >> + 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 DEBUG_SET_MODULE_RONX >> bool "Set loadable kernel module data as NX and text as RO" >> depends on MODULES >> diff --git a/arch/arm64/include/asm/ptdump.h b/arch/arm64/include/asm/ptdump.h >> index f72ee69..6afd847 100644 >> --- a/arch/arm64/include/asm/ptdump.h >> +++ b/arch/arm64/include/asm/ptdump.h >> @@ -42,5 +42,13 @@ static inline int ptdump_debugfs_register(struct ptdump_info *info, >> return 0; >> } >> #endif >> +void ptdump_check_wx(void); >> #endif /* CONFIG_ARM64_PTDUMP_CORE */ >> + >> +#ifdef CONFIG_DEBUG_WX >> +#define debug_checkwx() ptdump_check_wx() >> +#else >> +#define debug_checkwx() do { } while (0) >> +#endif >> + >> #endif /* __ASM_PTDUMP_H */ >> diff --git a/arch/arm64/mm/dump.c b/arch/arm64/mm/dump.c >> index bb36649..4913af5 100644 >> --- a/arch/arm64/mm/dump.c >> +++ b/arch/arm64/mm/dump.c >> @@ -74,6 +74,8 @@ struct pg_state { >> unsigned long start_address; >> unsigned level; >> u64 current_prot; >> + bool check_wx; >> + unsigned long wx_pages; >> }; >> >> struct prot_bits { >> @@ -202,6 +204,35 @@ static void dump_prot(struct pg_state *st, const struct prot_bits *bits, >> } >> } >> >> +static void note_prot_uxn(struct pg_state *st, unsigned long addr) >> +{ >> + if (!st->check_wx) >> + return; >> + >> + if ((st->current_prot & PTE_UXN) == PTE_UXN) >> + return; >> + >> + WARN_ONCE(1, "arm64/mm: Found non-UXN 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_prot_wx(struct pg_state *st, unsigned long addr) >> +{ >> + if (!st->check_wx) >> + return; >> + if ((st->current_prot & PTE_RDONLY) == PTE_RDONLY) >> + return; >> + if ((st->current_prot & PTE_PXN) == PTE_PXN) >> + return; >> + >> + WARN_ONCE(1, "arm64/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; >> +} >> + > > Why are these separate functions, and why is wx_pages increased twice, > potentially? > > Given how rare non-UXN kernel mappings should be, could we not just add > > if ((st->current_prot & PTE_UXN) == 0) > WARN(xxx) > > (without the _ONCE) to note_prot_wx(), and drop note_prot_uxn() entirely? > > UXN is a separate bit from PTE_PXN/PTE_RDONLY and both pairs need to be checked. The current return == 0 logic means that one set or the other may not get checked. Rather than complicate the logic, it seemed better to have separate functions. I see your point about the wx_pages double counting so I can fix that. >> static void note_page(struct pg_state *st, unsigned long addr, unsigned level, >> u64 val) >> { >> @@ -219,6 +250,8 @@ static void note_page(struct pg_state *st, unsigned long addr, unsigned level, >> unsigned long delta; >> >> if (st->current_prot) { >> + note_prot_uxn(st, addr); >> + note_prot_wx(st, addr); >> pt_dump_seq_printf(st->seq, "0x%016lx-0x%016lx ", >> st->start_address, addr); >> >> @@ -344,6 +377,25 @@ static struct ptdump_info kernel_ptdump_info = { >> .base_addr = VA_START, >> }; >> >> +void ptdump_check_wx(void) >> +{ >> + struct pg_state st = { >> + .seq = NULL, >> + .marker = (struct addr_marker[]) { >> + { -1, NULL}, >> + }, >> + .check_wx = true, >> + }; >> + >> + walk_pgd(&st, &init_mm, 0); >> + note_page(&st, 0, 0, 0); >> + if (st.wx_pages) >> + pr_info("Checked W+X mappings: FAILED, %lu W+X pages found\n", >> + st.wx_pages); > > Could we upgrade this to pr_warn? > Sure >> + else >> + pr_info("Checked W+X mappings: passed, no W+X pages found\n"); >> +} >> + >> static int ptdump_init(void) >> { >> ptdump_initialize(); >> diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c >> index 05615a3..2cbe2fe 100644 >> --- a/arch/arm64/mm/mmu.c >> +++ b/arch/arm64/mm/mmu.c >> @@ -42,6 +42,7 @@ >> #include <asm/tlb.h> >> #include <asm/memblock.h> >> #include <asm/mmu_context.h> >> +#include <asm/ptdump.h> >> >> u64 idmap_t0sz = TCR_T0SZ(VA_BITS); >> >> @@ -396,6 +397,7 @@ void mark_rodata_ro(void) >> section_size = (unsigned long)__init_begin - (unsigned long)__start_rodata; >> create_mapping_late(__pa(__start_rodata), (unsigned long)__start_rodata, >> section_size, PAGE_KERNEL_RO); >> + debug_checkwx(); >> } >> >> static void __init map_kernel_segment(pgd_t *pgd, void *va_start, void *va_end, >> -- >> 2.7.4 >>
diff --git a/arch/arm64/Kconfig.debug b/arch/arm64/Kconfig.debug index 21a5b74..d1ebd46 100644 --- a/arch/arm64/Kconfig.debug +++ b/arch/arm64/Kconfig.debug @@ -42,6 +42,35 @@ config ARM64_RANDOMIZE_TEXT_OFFSET of TEXT_OFFSET and platforms must not require a specific value. +config DEBUG_WX + bool "Warn on W+X mappings at boot" + select ARM64_PTDUMP_CORE + ---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. + This check also includes UXN, which should be set on all kernel + mappings. + + Look for a message in dmesg output like this: + + arm64/mm: Checked W+X mappings: passed, no W+X pages found. + + or like this, if the check failed: + + arm64/mm: Checked W+X mappings: FAILED, <N> W+X pages found. + + 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 DEBUG_SET_MODULE_RONX bool "Set loadable kernel module data as NX and text as RO" depends on MODULES diff --git a/arch/arm64/include/asm/ptdump.h b/arch/arm64/include/asm/ptdump.h index f72ee69..6afd847 100644 --- a/arch/arm64/include/asm/ptdump.h +++ b/arch/arm64/include/asm/ptdump.h @@ -42,5 +42,13 @@ static inline int ptdump_debugfs_register(struct ptdump_info *info, return 0; } #endif +void ptdump_check_wx(void); #endif /* CONFIG_ARM64_PTDUMP_CORE */ + +#ifdef CONFIG_DEBUG_WX +#define debug_checkwx() ptdump_check_wx() +#else +#define debug_checkwx() do { } while (0) +#endif + #endif /* __ASM_PTDUMP_H */ diff --git a/arch/arm64/mm/dump.c b/arch/arm64/mm/dump.c index bb36649..4913af5 100644 --- a/arch/arm64/mm/dump.c +++ b/arch/arm64/mm/dump.c @@ -74,6 +74,8 @@ struct pg_state { unsigned long start_address; unsigned level; u64 current_prot; + bool check_wx; + unsigned long wx_pages; }; struct prot_bits { @@ -202,6 +204,35 @@ static void dump_prot(struct pg_state *st, const struct prot_bits *bits, } } +static void note_prot_uxn(struct pg_state *st, unsigned long addr) +{ + if (!st->check_wx) + return; + + if ((st->current_prot & PTE_UXN) == PTE_UXN) + return; + + WARN_ONCE(1, "arm64/mm: Found non-UXN 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_prot_wx(struct pg_state *st, unsigned long addr) +{ + if (!st->check_wx) + return; + if ((st->current_prot & PTE_RDONLY) == PTE_RDONLY) + return; + if ((st->current_prot & PTE_PXN) == PTE_PXN) + return; + + WARN_ONCE(1, "arm64/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 level, u64 val) { @@ -219,6 +250,8 @@ static void note_page(struct pg_state *st, unsigned long addr, unsigned level, unsigned long delta; if (st->current_prot) { + note_prot_uxn(st, addr); + note_prot_wx(st, addr); pt_dump_seq_printf(st->seq, "0x%016lx-0x%016lx ", st->start_address, addr); @@ -344,6 +377,25 @@ static struct ptdump_info kernel_ptdump_info = { .base_addr = VA_START, }; +void ptdump_check_wx(void) +{ + struct pg_state st = { + .seq = NULL, + .marker = (struct addr_marker[]) { + { -1, NULL}, + }, + .check_wx = true, + }; + + walk_pgd(&st, &init_mm, 0); + note_page(&st, 0, 0, 0); + if (st.wx_pages) + pr_info("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"); +} + static int ptdump_init(void) { ptdump_initialize(); diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c index 05615a3..2cbe2fe 100644 --- a/arch/arm64/mm/mmu.c +++ b/arch/arm64/mm/mmu.c @@ -42,6 +42,7 @@ #include <asm/tlb.h> #include <asm/memblock.h> #include <asm/mmu_context.h> +#include <asm/ptdump.h> u64 idmap_t0sz = TCR_T0SZ(VA_BITS); @@ -396,6 +397,7 @@ void mark_rodata_ro(void) section_size = (unsigned long)__init_begin - (unsigned long)__start_rodata; create_mapping_late(__pa(__start_rodata), (unsigned long)__start_rodata, section_size, PAGE_KERNEL_RO); + debug_checkwx(); } static void __init map_kernel_segment(pgd_t *pgd, void *va_start, void *va_end,
Page mappings with full RWX permissions are a security risk. x86 has an option to walk the page tables and dump any bad pages. (See e1a58320a38d ("x86/mm: Warn on W^X mappings")). Add a similar implementation for arm64. Reviewed-by: Kees Cook <keescook@chromium.org> Reviewed-by: Mark Rutland <mark.rutland@arm.com> Tested-by: Mark Rutland <mark.rutland@arm.com> Signed-off-by: Laura Abbott <labbott@redhat.com> --- v3: Rebased for header guard fixup, whitespace fixes --- arch/arm64/Kconfig.debug | 29 +++++++++++++++++++++++ arch/arm64/include/asm/ptdump.h | 8 +++++++ arch/arm64/mm/dump.c | 52 +++++++++++++++++++++++++++++++++++++++++ arch/arm64/mm/mmu.c | 2 ++ 4 files changed, 91 insertions(+)