* [PATCH 0/2] objtool uaccess fixes @ 2019-04-24 7:19 Peter Zijlstra 2019-04-24 7:19 ` [PATCH 1/2] x86/uaccess: Dont leak the AC flag into __put_user() argument evaluation Peter Zijlstra 2019-04-24 7:19 ` [PATCH 2/2] mm/uaccess: Use unsigned long Peter Zijlstra 0 siblings, 2 replies; 5+ messages in thread From: Peter Zijlstra @ 2019-04-24 7:19 UTC (permalink / raw) To: mingo, tglx, x86; +Cc: linux-kernel, luto, peterz Hi, Here the two patches required to build a clean x86_64-allyesconfig with older GCC (<8). ^ permalink raw reply [flat|nested] 5+ messages in thread
* [PATCH 1/2] x86/uaccess: Dont leak the AC flag into __put_user() argument evaluation 2019-04-24 7:19 [PATCH 0/2] objtool uaccess fixes Peter Zijlstra @ 2019-04-24 7:19 ` Peter Zijlstra 2019-04-24 11:10 ` [tip:core/objtool] " tip-bot for Peter Zijlstra 2019-04-24 7:19 ` [PATCH 2/2] mm/uaccess: Use unsigned long Peter Zijlstra 1 sibling, 1 reply; 5+ messages in thread From: Peter Zijlstra @ 2019-04-24 7:19 UTC (permalink / raw) To: mingo, tglx, x86; +Cc: linux-kernel, luto, peterz, Randy Dunlap, Linus Torvalds The __put_user() macro evaluates it's @ptr argument inside the __uaccess_begin() / __uaccess_end() region. While this would normally not be expected to be an issue, an UBSAN bug (it ignored -fwrapv, fixed in GCC 8+) would transform the @ptr evaluation for: drivers/gpu/drm/i915/i915_gem_execbuffer.c: if (unlikely(__put_user(offset, &urelocs[r-stack].presumed_offset))) { into a signed-overflow-UB check and trigger the objtool AC validation. Finish commit 2a418cf3f5f1 ("x86/uaccess: Don't leak the AC flag into __put_user() value evaluation") and explicitly evaluate all 3 argument early. Reported-by: Randy Dunlap <rdunlap@infradead.org> Acked-by: Randy Dunlap <rdunlap@infradead.org> # build-tested Acked-by: Linus Torvalds <torvalds@linux-foundation.org> Fixes: 2a418cf3f5f1 ("x86/uaccess: Don't leak the AC flag into __put_user() value evaluation") Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> --- arch/x86/include/asm/uaccess.h | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-) --- a/arch/x86/include/asm/uaccess.h +++ b/arch/x86/include/asm/uaccess.h @@ -427,10 +427,11 @@ do { \ ({ \ __label__ __pu_label; \ int __pu_err = -EFAULT; \ - __typeof__(*(ptr)) __pu_val; \ - __pu_val = x; \ + __typeof__(*(ptr)) __pu_val = (x); \ + __typeof__(ptr) __pu_ptr = (ptr); \ + __typeof__(size) __pu_size = (size); \ __uaccess_begin(); \ - __put_user_size(__pu_val, (ptr), (size), __pu_label); \ + __put_user_size(__pu_val, __pu_ptr, __pu_size, __pu_label); \ __pu_err = 0; \ __pu_label: \ __uaccess_end(); \ ^ permalink raw reply [flat|nested] 5+ messages in thread
* [tip:core/objtool] x86/uaccess: Dont leak the AC flag into __put_user() argument evaluation 2019-04-24 7:19 ` [PATCH 1/2] x86/uaccess: Dont leak the AC flag into __put_user() argument evaluation Peter Zijlstra @ 2019-04-24 11:10 ` tip-bot for Peter Zijlstra 0 siblings, 0 replies; 5+ messages in thread From: tip-bot for Peter Zijlstra @ 2019-04-24 11:10 UTC (permalink / raw) To: linux-tip-commits Cc: rdunlap, mingo, torvalds, linux-kernel, peterz, hpa, tglx Commit-ID: 6ae865615fc43d014da2fd1f1bba7e81ee622d1b Gitweb: https://git.kernel.org/tip/6ae865615fc43d014da2fd1f1bba7e81ee622d1b Author: Peter Zijlstra <peterz@infradead.org> AuthorDate: Wed, 24 Apr 2019 09:19:24 +0200 Committer: Ingo Molnar <mingo@kernel.org> CommitDate: Wed, 24 Apr 2019 12:19:45 +0200 x86/uaccess: Dont leak the AC flag into __put_user() argument evaluation The __put_user() macro evaluates it's @ptr argument inside the __uaccess_begin() / __uaccess_end() region. While this would normally not be expected to be an issue, an UBSAN bug (it ignored -fwrapv, fixed in GCC 8+) would transform the @ptr evaluation for: drivers/gpu/drm/i915/i915_gem_execbuffer.c: if (unlikely(__put_user(offset, &urelocs[r-stack].presumed_offset))) { into a signed-overflow-UB check and trigger the objtool AC validation. Finish this commit: 2a418cf3f5f1 ("x86/uaccess: Don't leak the AC flag into __put_user() value evaluation") and explicitly evaluate all 3 arguments early. Reported-by: Randy Dunlap <rdunlap@infradead.org> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Acked-by: Randy Dunlap <rdunlap@infradead.org> # build-tested Acked-by: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: luto@kernel.org Fixes: 2a418cf3f5f1 ("x86/uaccess: Don't leak the AC flag into __put_user() value evaluation") Link: http://lkml.kernel.org/r/20190424072208.695962771@infradead.org Signed-off-by: Ingo Molnar <mingo@kernel.org> --- arch/x86/include/asm/uaccess.h | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-) diff --git a/arch/x86/include/asm/uaccess.h b/arch/x86/include/asm/uaccess.h index 5ca7b91faf67..bb21913885a3 100644 --- a/arch/x86/include/asm/uaccess.h +++ b/arch/x86/include/asm/uaccess.h @@ -427,10 +427,11 @@ do { \ ({ \ __label__ __pu_label; \ int __pu_err = -EFAULT; \ - __typeof__(*(ptr)) __pu_val; \ - __pu_val = x; \ + __typeof__(*(ptr)) __pu_val = (x); \ + __typeof__(ptr) __pu_ptr = (ptr); \ + __typeof__(size) __pu_size = (size); \ __uaccess_begin(); \ - __put_user_size(__pu_val, (ptr), (size), __pu_label); \ + __put_user_size(__pu_val, __pu_ptr, __pu_size, __pu_label); \ __pu_err = 0; \ __pu_label: \ __uaccess_end(); \ ^ permalink raw reply related [flat|nested] 5+ messages in thread
* [PATCH 2/2] mm/uaccess: Use unsigned long 2019-04-24 7:19 [PATCH 0/2] objtool uaccess fixes Peter Zijlstra 2019-04-24 7:19 ` [PATCH 1/2] x86/uaccess: Dont leak the AC flag into __put_user() argument evaluation Peter Zijlstra @ 2019-04-24 7:19 ` Peter Zijlstra 2019-04-24 11:10 ` [tip:core/objtool] mm/uaccess: Use 'unsigned long' to placate UBSAN warnings on older GCC versions tip-bot for Peter Zijlstra 1 sibling, 1 reply; 5+ messages in thread From: Peter Zijlstra @ 2019-04-24 7:19 UTC (permalink / raw) To: mingo, tglx, x86; +Cc: linux-kernel, luto, peterz, Randy Dunlap, Linus Torvalds Randy reported objtool triggered on his (GCC-7.4) build: lib/strncpy_from_user.o: warning: objtool: strncpy_from_user()+0x315: call to __ubsan_handle_add_overflow() with UACCESS enabled lib/strnlen_user.o: warning: objtool: strnlen_user()+0x337: call to __ubsan_handle_sub_overflow() with UACCESS enabled This is due to UBSAN generating signed-overflow-UB warnings where it should not. Prior to GCC-8 UBSAN ignored -fwrapv (which the kernel uses through -fno-strict-overflow). Make the functions use 'unsigned long' throughout. Reported-by: Randy Dunlap <rdunlap@infradead.org> Acked-by: Randy Dunlap <rdunlap@infradead.org> # build-tested Acked-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> --- lib/strncpy_from_user.c | 5 +++-- lib/strnlen_user.c | 4 ++-- 2 files changed, 5 insertions(+), 4 deletions(-) --- a/lib/strncpy_from_user.c +++ b/lib/strncpy_from_user.c @@ -23,10 +23,11 @@ * hit it), 'max' is the address space maximum (and we return * -EFAULT if we hit it). */ -static inline long do_strncpy_from_user(char *dst, const char __user *src, long count, unsigned long max) +static inline long do_strncpy_from_user(char *dst, const char __user *src, + unsigned long count, unsigned long max) { const struct word_at_a_time constants = WORD_AT_A_TIME_CONSTANTS; - long res = 0; + unsigned long res = 0; /* * Truncate 'max' to the user-specified limit, so that --- a/lib/strnlen_user.c +++ b/lib/strnlen_user.c @@ -28,7 +28,7 @@ static inline long do_strnlen_user(const char __user *src, unsigned long count, unsigned long max) { const struct word_at_a_time constants = WORD_AT_A_TIME_CONSTANTS; - long align, res = 0; + unsigned long align, res = 0; unsigned long c; /* @@ -42,7 +42,7 @@ static inline long do_strnlen_user(const * Do everything aligned. But that means that we * need to also expand the maximum.. */ - align = (sizeof(long) - 1) & (unsigned long)src; + align = (sizeof(unsigned long) - 1) & (unsigned long)src; src -= align; max += align; ^ permalink raw reply [flat|nested] 5+ messages in thread
* [tip:core/objtool] mm/uaccess: Use 'unsigned long' to placate UBSAN warnings on older GCC versions 2019-04-24 7:19 ` [PATCH 2/2] mm/uaccess: Use unsigned long Peter Zijlstra @ 2019-04-24 11:10 ` tip-bot for Peter Zijlstra 0 siblings, 0 replies; 5+ messages in thread From: tip-bot for Peter Zijlstra @ 2019-04-24 11:10 UTC (permalink / raw) To: linux-tip-commits Cc: rdunlap, peterz, linux-kernel, torvalds, hpa, tglx, mingo Commit-ID: 29da93fea3ea39ab9b12270cc6be1b70ef201c9e Gitweb: https://git.kernel.org/tip/29da93fea3ea39ab9b12270cc6be1b70ef201c9e Author: Peter Zijlstra <peterz@infradead.org> AuthorDate: Wed, 24 Apr 2019 09:19:25 +0200 Committer: Ingo Molnar <mingo@kernel.org> CommitDate: Wed, 24 Apr 2019 12:19:45 +0200 mm/uaccess: Use 'unsigned long' to placate UBSAN warnings on older GCC versions Randy reported objtool triggered on his (GCC-7.4) build: lib/strncpy_from_user.o: warning: objtool: strncpy_from_user()+0x315: call to __ubsan_handle_add_overflow() with UACCESS enabled lib/strnlen_user.o: warning: objtool: strnlen_user()+0x337: call to __ubsan_handle_sub_overflow() with UACCESS enabled This is due to UBSAN generating signed-overflow-UB warnings where it should not. Prior to GCC-8 UBSAN ignored -fwrapv (which the kernel uses through -fno-strict-overflow). Make the functions use 'unsigned long' throughout. Reported-by: Randy Dunlap <rdunlap@infradead.org> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Acked-by: Randy Dunlap <rdunlap@infradead.org> # build-tested Acked-by: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: luto@kernel.org Link: http://lkml.kernel.org/r/20190424072208.754094071@infradead.org Signed-off-by: Ingo Molnar <mingo@kernel.org> --- lib/strncpy_from_user.c | 5 +++-- lib/strnlen_user.c | 4 ++-- 2 files changed, 5 insertions(+), 4 deletions(-) diff --git a/lib/strncpy_from_user.c b/lib/strncpy_from_user.c index 58eacd41526c..023ba9f3b99f 100644 --- a/lib/strncpy_from_user.c +++ b/lib/strncpy_from_user.c @@ -23,10 +23,11 @@ * hit it), 'max' is the address space maximum (and we return * -EFAULT if we hit it). */ -static inline long do_strncpy_from_user(char *dst, const char __user *src, long count, unsigned long max) +static inline long do_strncpy_from_user(char *dst, const char __user *src, + unsigned long count, unsigned long max) { const struct word_at_a_time constants = WORD_AT_A_TIME_CONSTANTS; - long res = 0; + unsigned long res = 0; /* * Truncate 'max' to the user-specified limit, so that diff --git a/lib/strnlen_user.c b/lib/strnlen_user.c index 1c1a1b0e38a5..7f2db3fe311f 100644 --- a/lib/strnlen_user.c +++ b/lib/strnlen_user.c @@ -28,7 +28,7 @@ static inline long do_strnlen_user(const char __user *src, unsigned long count, unsigned long max) { const struct word_at_a_time constants = WORD_AT_A_TIME_CONSTANTS; - long align, res = 0; + unsigned long align, res = 0; unsigned long c; /* @@ -42,7 +42,7 @@ static inline long do_strnlen_user(const char __user *src, unsigned long count, * Do everything aligned. But that means that we * need to also expand the maximum.. */ - align = (sizeof(long) - 1) & (unsigned long)src; + align = (sizeof(unsigned long) - 1) & (unsigned long)src; src -= align; max += align; ^ permalink raw reply related [flat|nested] 5+ messages in thread
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