| Message ID | 90667b2b7f773308318261f96ebefd1a67133c4c.1732464395.git.lukas@wunner.de (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | [for-next/fixes] arm64/mm: Fix false-positive !virt_addr_valid() for kernel image | expand |
On Sun, 24 Nov 2024 at 17:16, Lukas Wunner <lukas@wunner.de> wrote: > > Zorro reports a false-positive BUG_ON() when running crypto selftests on > boot: Since commit 1e562deacecc ("crypto: rsassa-pkcs1 - Migrate to > sig_alg backend"), test_sig_one() invokes an RSA verify operation with a > test vector in the kernel's .rodata section. The test vector is passed > to sg_set_buf(), which performs a virt_addr_valid() check. > > On arm64, virt_addr_valid() returns false for kernel image addresses > such as this one, even though they're valid virtual addresses. > x86 returns true for kernel image addresses, so the BUG_ON() does not > occur there. In fact, x86 has been doing so for 16 years, i.e. since > commit af5c2bd16ac2 ("x86: fix virt_addr_valid() with > CONFIG_DEBUG_VIRTUAL=y, v2"). > > Do the same on arm64 to avoid the false-positive BUG_ON() and to achieve > consistent virt_addr_valid() behavior across arches. > > Silence a WARN splat in __virt_to_phys() which occurs once the BUG_ON() > is avoided. > > The is_kernel_address() helper introduced herein cannot be put directly > in the virt_addr_valid() macro: It has to be part of the kernel proper > so that it has visibility of the _text and _end symbols (referenced > through KERNEL_START and KERNEL_END). These symbols are not exported, > so modules expanding the virt_addr_valid() macro could not access them. > For almost all invocations of virt_addr_valid(), __is_lm_address() > returns true, so jumping to the is_kernel_address() helper hardly ever > occurs and its performance impact is thus negligible. > > Likewise, calling is_kernel_address() from the functions in physaddr.c > ought to be fine as they depend on CONFIG_DEBUG_VIRTUAL=y, which is > explicitly described as "costly" in the Kconfig help text. (And this > doesn't add much cost really.) > > Abridged stack trace: > > kernel BUG at include/linux/scatterlist.h:187! > sg_init_one() > rsassa_pkcs1_verify() > test_sig_one() > alg_test_sig() > alg_test() > cryptomgr_test() > > Fixes: 1e562deacecc ("crypto: rsassa-pkcs1 - Migrate to sig_alg backend") > Reported-by: Zorro Lang <zlang@redhat.com> > Closes: https://lore.kernel.org/r/20241122045106.tzhvm2wrqvttub6k@dell-per750-06-vm-08.rhts.eng.pek2.redhat.com/ > Signed-off-by: Lukas Wunner <lukas@wunner.de> > --- > Just from looking at the code it seems arm's virt_addr_valid() returns > true for kernel image addresses, so apparently arm64 is the odd man out. > That is because ARM maps the kernel in the linear map, whereas arm64 maps the kernel in the vmalloc space. vmalloc addresses cannot be used for DMA, which is why virt_addr_valid() rejects them. On arm64, the same applies to the kernel image, as well as the vmap'ed stack. > Note that this fix would have obviated the need for commit c02e7c5c6da8 > ("arm64/mm: use lm_alias() with addresses passed to memblock_free()"). > Your 'fix' will break other stuff: it is used, e.g., to decide whether __pa() may be used on the input VA, which applies a fixed translation on the input, rather than walk the page tables to obtain the physical address. > arch/arm64/include/asm/memory.h | 6 +++++- > arch/arm64/mm/init.c | 7 +++++++ > arch/arm64/mm/physaddr.c | 6 +++--- > 3 files changed, 15 insertions(+), 4 deletions(-) > > diff --git a/arch/arm64/include/asm/memory.h b/arch/arm64/include/asm/memory.h > index b9b9929..bb83315 100644 > --- a/arch/arm64/include/asm/memory.h > +++ b/arch/arm64/include/asm/memory.h > @@ -416,9 +416,13 @@ static inline unsigned long virt_to_pfn(const void *kaddr) > }) > #endif /* CONFIG_DEBUG_VIRTUAL */ > > +bool is_kernel_address(unsigned long x); > + > #define virt_addr_valid(addr) ({ \ > __typeof__(addr) __addr = __tag_reset(addr); \ > - __is_lm_address(__addr) && pfn_is_map_memory(virt_to_pfn(__addr)); \ > + (__is_lm_address(__addr) || \ > + is_kernel_address((unsigned long)__addr)) && \ > + pfn_is_map_memory(virt_to_pfn(__addr)); \ > }) > > void dump_mem_limit(void); > diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c > index d21f67d..2e8a00f 100644 > --- a/arch/arm64/mm/init.c > +++ b/arch/arm64/mm/init.c > @@ -156,6 +156,13 @@ static void __init zone_sizes_init(void) > free_area_init(max_zone_pfns); > } > > +bool is_kernel_address(unsigned long x) > +{ > + return x >= (unsigned long) KERNEL_START && > + x <= (unsigned long) KERNEL_END; > +} > +EXPORT_SYMBOL(is_kernel_address); > + > int pfn_is_map_memory(unsigned long pfn) > { > phys_addr_t addr = PFN_PHYS(pfn); > diff --git a/arch/arm64/mm/physaddr.c b/arch/arm64/mm/physaddr.c > index cde44c1..2d6755b 100644 > --- a/arch/arm64/mm/physaddr.c > +++ b/arch/arm64/mm/physaddr.c > @@ -9,7 +9,8 @@ > > phys_addr_t __virt_to_phys(unsigned long x) > { > - WARN(!__is_lm_address(__tag_reset(x)), > + WARN(!__is_lm_address(__tag_reset(x)) && > + !is_kernel_address(__tag_reset(x)), > "virt_to_phys used for non-linear address: %pK (%pS)\n", > (void *)x, > (void *)x); > @@ -24,8 +25,7 @@ phys_addr_t __phys_addr_symbol(unsigned long x) > * This is bounds checking against the kernel image only. > * __pa_symbol should only be used on kernel symbol addresses. > */ > - VIRTUAL_BUG_ON(x < (unsigned long) KERNEL_START || > - x > (unsigned long) KERNEL_END); > + VIRTUAL_BUG_ON(!is_kernel_address(x)); > return __pa_symbol_nodebug(x); > } > EXPORT_SYMBOL(__phys_addr_symbol); > -- > 2.43.0 > >
On Sun, 24 Nov 2024 at 17:38, Ard Biesheuvel <ardb@kernel.org> wrote: > > On Sun, 24 Nov 2024 at 17:16, Lukas Wunner <lukas@wunner.de> wrote: > > > > Zorro reports a false-positive BUG_ON() when running crypto selftests on > > boot: Since commit 1e562deacecc ("crypto: rsassa-pkcs1 - Migrate to > > sig_alg backend"), test_sig_one() invokes an RSA verify operation with a > > test vector in the kernel's .rodata section. The test vector is passed > > to sg_set_buf(), which performs a virt_addr_valid() check. > > > > On arm64, virt_addr_valid() returns false for kernel image addresses > > such as this one, even though they're valid virtual addresses. > > x86 returns true for kernel image addresses, so the BUG_ON() does not > > occur there. In fact, x86 has been doing so for 16 years, i.e. since > > commit af5c2bd16ac2 ("x86: fix virt_addr_valid() with > > CONFIG_DEBUG_VIRTUAL=y, v2"). > > > > Do the same on arm64 to avoid the false-positive BUG_ON() and to achieve > > consistent virt_addr_valid() behavior across arches. > > > > Silence a WARN splat in __virt_to_phys() which occurs once the BUG_ON() > > is avoided. > > > > The is_kernel_address() helper introduced herein cannot be put directly > > in the virt_addr_valid() macro: It has to be part of the kernel proper > > so that it has visibility of the _text and _end symbols (referenced > > through KERNEL_START and KERNEL_END). These symbols are not exported, > > so modules expanding the virt_addr_valid() macro could not access them. > > For almost all invocations of virt_addr_valid(), __is_lm_address() > > returns true, so jumping to the is_kernel_address() helper hardly ever > > occurs and its performance impact is thus negligible. > > > > Likewise, calling is_kernel_address() from the functions in physaddr.c > > ought to be fine as they depend on CONFIG_DEBUG_VIRTUAL=y, which is > > explicitly described as "costly" in the Kconfig help text. (And this > > doesn't add much cost really.) > > > > Abridged stack trace: > > > > kernel BUG at include/linux/scatterlist.h:187! > > sg_init_one() > > rsassa_pkcs1_verify() > > test_sig_one() > > alg_test_sig() > > alg_test() > > cryptomgr_test() > > > > Fixes: 1e562deacecc ("crypto: rsassa-pkcs1 - Migrate to sig_alg backend") > > Reported-by: Zorro Lang <zlang@redhat.com> > > Closes: https://lore.kernel.org/r/20241122045106.tzhvm2wrqvttub6k@dell-per750-06-vm-08.rhts.eng.pek2.redhat.com/ > > Signed-off-by: Lukas Wunner <lukas@wunner.de> > > --- > > Just from looking at the code it seems arm's virt_addr_valid() returns > > true for kernel image addresses, so apparently arm64 is the odd man out. > > > > That is because ARM maps the kernel in the linear map, whereas arm64 > maps the kernel in the vmalloc space. > > vmalloc addresses cannot be used for DMA, which is why > virt_addr_valid() rejects them. On arm64, the same applies to the > kernel image, as well as the vmap'ed stack. > > > Note that this fix would have obviated the need for commit c02e7c5c6da8 > > ("arm64/mm: use lm_alias() with addresses passed to memblock_free()"). > > > > Your 'fix' will break other stuff: it is used, e.g., to decide whether > __pa() may be used on the input VA, which applies a fixed translation > on the input, rather than walk the page tables to obtain the physical > address. > Apologies, I replied a little too quickly. __pa() on arm64 permits linear addresses and kernel image addresses, and so the kernel image is treated differently from the vmap'ed stack and other vmalloc addresses. However, that doesn't mean doing DMA from the kernel image is a great idea. Allocations in the linear map are rounded up to cacheline size to ensure that they are safe for non-coherent DMA, but this does not apply to the kernel image. .rodata should still be safe in this regard, but the general idea of allowing kernel image addresses in places where DMA'able virtual addresses are expected is something we should consider with care.
On Mon, Nov 25, 2024 at 10:54:49AM +0100, Lukas Wunner wrote: > On Sun, Nov 24, 2024 at 06:13:26PM +0100, Ard Biesheuvel wrote: > > > On Sun, 24 Nov 2024 at 17:16, Lukas Wunner <lukas@wunner.de> wrote: > > > > Zorro reports a false-positive BUG_ON() when running crypto selftests on > > > > boot: Since commit 1e562deacecc ("crypto: rsassa-pkcs1 - Migrate to > > > > sig_alg backend"), test_sig_one() invokes an RSA verify operation with a > > > > test vector in the kernel's .rodata section. The test vector is passed > > > > to sg_set_buf(), which performs a virt_addr_valid() check. > > > > > > > > On arm64, virt_addr_valid() returns false for kernel image addresses > > > > such as this one, even though they're valid virtual addresses. > > > > x86 returns true for kernel image addresses, so the BUG_ON() does not > > > > occur there. In fact, x86 has been doing so for 16 years, i.e. since > > > > commit af5c2bd16ac2 ("x86: fix virt_addr_valid() with > > > > CONFIG_DEBUG_VIRTUAL=y, v2"). > > > > > > > > Do the same on arm64 to avoid the false-positive BUG_ON() and to achieve > > > > consistent virt_addr_valid() behavior across arches. > [...] > > that doesn't mean doing DMA from the kernel image is a great > > idea. Allocations in the linear map are rounded up to cacheline size > > to ensure that they are safe for non-coherent DMA, but this does not > > apply to the kernel image. .rodata should still be safe in this > > regard, but the general idea of allowing kernel image addresses in > > places where DMA'able virtual addresses are expected is something we > > should consider with care. > > Other arches do not seem to be concerned about this and > let virt_addr_valid() return true for the kernel image. > It's not clear why arm64 is special and needs to return false. > > However, I agree there's hardly ever a reason to DMA from/to the > .text section. From a security perspective, constraining this to > .rodata seems reasonable to me and I'll be happy to amend the patch > to that effect if that's the consensus. Instead, can we update the test to use lm_alias() on the symbols in question? That'll convert a kernel image address to its linear map alias, and then that'll work with virt_addr_valid(), virt_to_phys(), etc. I don't think it's generally a good idea to relax virt_addr_valid() to accept addresses outside of the linear map, regardless of what other architectures do. We've had issues in the past with broken conversions, and the fixups in virt_to_phys() is really only there as a best-effort way to not crash and allow the warning messages to get out. Mark.
On Mon, Nov 25, 2024 at 03:49:10PM +0100, Lukas Wunner wrote: > On Mon, Nov 25, 2024 at 10:50:48AM +0000, Mark Rutland wrote: > > On Mon, Nov 25, 2024 at 10:54:49AM +0100, Lukas Wunner wrote: > > > Other arches do not seem to be concerned about this and > > > let virt_addr_valid() return true for the kernel image. > > > It's not clear why arm64 is special and needs to return false. > > > > > > However, I agree there's hardly ever a reason to DMA from/to the > > > .text section. From a security perspective, constraining this to > > > .rodata seems reasonable to me and I'll be happy to amend the patch > > > to that effect if that's the consensus. > > > > Instead, can we update the test to use lm_alias() on the symbols in > > question? That'll convert a kernel image address to its linear map > > alias, and then that'll work with virt_addr_valid(), virt_to_phys(), > > etc. > > Do you mean that sg_set_buf() should pass the address to lm_alias() > if it points into the kernel image? No; I meant that the test could use lm_alias() on the test vectors before passing those to sg_set_buf(), when the test code knows by construction that those vectors happen to be part of the kernel image. That'll work on all architectures. That said, looking at the code it appears that testmgr.c can be built as a module, so the test vectors could be module/vmalloc addresses rather than virt/linear or image addresses. Given that, I don't think the changes suggested here are sufficient, as module addresses should still be rejected. Can we kmemdup() the test vector data first? That'd give us a legitimate virt/linear address that we can use. > That would require a helper to determine whether it's a kernel image > address or not. It seems we do not have such a cross-architecture > helper (but maybe I'm missing something). (I am adding an arm64-specific > one in the proposed patch.) > > So this doesn't look like a viable approach. > > Also, I'd expect pushback against an sg_set_buf() change which is > only necessary to accommodate arm64. I'd expect the obvious question > to be asked, which is why arm64's virt_addr_valid() can't behave like > any other architecture's. And honestly I wouldn't know what to answer. I don't think arm64 is doing anything wrong here; an image address is *not* a virt/linear address, and we only fix that up in virt_to_*() as a best-effort thing. I think other architectures which accept that are signing themselves up for subtle bugs that we're trying to prevent early. Mark.
diff --git a/arch/arm64/include/asm/memory.h b/arch/arm64/include/asm/memory.h index b9b9929..bb83315 100644 --- a/arch/arm64/include/asm/memory.h +++ b/arch/arm64/include/asm/memory.h @@ -416,9 +416,13 @@ static inline unsigned long virt_to_pfn(const void *kaddr) }) #endif /* CONFIG_DEBUG_VIRTUAL */ +bool is_kernel_address(unsigned long x); + #define virt_addr_valid(addr) ({ \ __typeof__(addr) __addr = __tag_reset(addr); \ - __is_lm_address(__addr) && pfn_is_map_memory(virt_to_pfn(__addr)); \ + (__is_lm_address(__addr) || \ + is_kernel_address((unsigned long)__addr)) && \ + pfn_is_map_memory(virt_to_pfn(__addr)); \ }) void dump_mem_limit(void); diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c index d21f67d..2e8a00f 100644 --- a/arch/arm64/mm/init.c +++ b/arch/arm64/mm/init.c @@ -156,6 +156,13 @@ static void __init zone_sizes_init(void) free_area_init(max_zone_pfns); } +bool is_kernel_address(unsigned long x) +{ + return x >= (unsigned long) KERNEL_START && + x <= (unsigned long) KERNEL_END; +} +EXPORT_SYMBOL(is_kernel_address); + int pfn_is_map_memory(unsigned long pfn) { phys_addr_t addr = PFN_PHYS(pfn); diff --git a/arch/arm64/mm/physaddr.c b/arch/arm64/mm/physaddr.c index cde44c1..2d6755b 100644 --- a/arch/arm64/mm/physaddr.c +++ b/arch/arm64/mm/physaddr.c @@ -9,7 +9,8 @@ phys_addr_t __virt_to_phys(unsigned long x) { - WARN(!__is_lm_address(__tag_reset(x)), + WARN(!__is_lm_address(__tag_reset(x)) && + !is_kernel_address(__tag_reset(x)), "virt_to_phys used for non-linear address: %pK (%pS)\n", (void *)x, (void *)x); @@ -24,8 +25,7 @@ phys_addr_t __phys_addr_symbol(unsigned long x) * This is bounds checking against the kernel image only. * __pa_symbol should only be used on kernel symbol addresses. */ - VIRTUAL_BUG_ON(x < (unsigned long) KERNEL_START || - x > (unsigned long) KERNEL_END); + VIRTUAL_BUG_ON(!is_kernel_address(x)); return __pa_symbol_nodebug(x); } EXPORT_SYMBOL(__phys_addr_symbol);
Zorro reports a false-positive BUG_ON() when running crypto selftests on boot: Since commit 1e562deacecc ("crypto: rsassa-pkcs1 - Migrate to sig_alg backend"), test_sig_one() invokes an RSA verify operation with a test vector in the kernel's .rodata section. The test vector is passed to sg_set_buf(), which performs a virt_addr_valid() check. On arm64, virt_addr_valid() returns false for kernel image addresses such as this one, even though they're valid virtual addresses. x86 returns true for kernel image addresses, so the BUG_ON() does not occur there. In fact, x86 has been doing so for 16 years, i.e. since commit af5c2bd16ac2 ("x86: fix virt_addr_valid() with CONFIG_DEBUG_VIRTUAL=y, v2"). Do the same on arm64 to avoid the false-positive BUG_ON() and to achieve consistent virt_addr_valid() behavior across arches. Silence a WARN splat in __virt_to_phys() which occurs once the BUG_ON() is avoided. The is_kernel_address() helper introduced herein cannot be put directly in the virt_addr_valid() macro: It has to be part of the kernel proper so that it has visibility of the _text and _end symbols (referenced through KERNEL_START and KERNEL_END). These symbols are not exported, so modules expanding the virt_addr_valid() macro could not access them. For almost all invocations of virt_addr_valid(), __is_lm_address() returns true, so jumping to the is_kernel_address() helper hardly ever occurs and its performance impact is thus negligible. Likewise, calling is_kernel_address() from the functions in physaddr.c ought to be fine as they depend on CONFIG_DEBUG_VIRTUAL=y, which is explicitly described as "costly" in the Kconfig help text. (And this doesn't add much cost really.) Abridged stack trace: kernel BUG at include/linux/scatterlist.h:187! sg_init_one() rsassa_pkcs1_verify() test_sig_one() alg_test_sig() alg_test() cryptomgr_test() Fixes: 1e562deacecc ("crypto: rsassa-pkcs1 - Migrate to sig_alg backend") Reported-by: Zorro Lang <zlang@redhat.com> Closes: https://lore.kernel.org/r/20241122045106.tzhvm2wrqvttub6k@dell-per750-06-vm-08.rhts.eng.pek2.redhat.com/ Signed-off-by: Lukas Wunner <lukas@wunner.de> --- Just from looking at the code it seems arm's virt_addr_valid() returns true for kernel image addresses, so apparently arm64 is the odd man out. Note that this fix would have obviated the need for commit c02e7c5c6da8 ("arm64/mm: use lm_alias() with addresses passed to memblock_free()"). arch/arm64/include/asm/memory.h | 6 +++++- arch/arm64/mm/init.c | 7 +++++++ arch/arm64/mm/physaddr.c | 6 +++--- 3 files changed, 15 insertions(+), 4 deletions(-)