objtool uaccess fixes
Subsystems (2)
cover objtool uaccess fixes
Hi,
Here the two patches required to build a clean x86_64-allyesconfig with older GCC (<8).
PATCH 1/2 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 commit 2a418cf3f5f1 ("x86/uaccess: Don't leak the AC flag into __put_user() value evaluation") and explicitly evaluate all 3 argument early.
--- arch/x86/include/asm/uaccess.h | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-)
arch/x86/include/asm/uaccess.h +4 -3
@@ -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(); \
tip-bot for Peter Zijlstra
merge bot[tip:core/objtool] x86/uaccess: Dont leak the AC flag into __put_user() argument evaluation
x86/uaccess: Dont leak the AC flag into __put_user() argument evaluation
Commit-ID: 6ae865615fc43d014da2fd1f1bba7e81ee622d1b Gitweb: https://git.kernel.org/tip/6ae865615fc43d014da2fd1f1bba7e81ee622d1b Author: Peter Zijlstra <[email protected]> AuthorDate: Wed, 24 Apr 2019 09:19:24 +0200 Committer: Ingo Molnar <[email protected]> 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.
--- arch/x86/include/asm/uaccess.h | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-)
arch/x86/include/asm/uaccess.h +4 -3
@@ -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(); \
PATCH 2/2 mm/uaccess: Use unsigned long
In reply to Peter ZijlstraRandy 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.
--- lib/strncpy_from_user.c | 5 +++-- lib/strnlen_user.c | 4 ++-- 2 files changed, 5 insertions(+), 4 deletions(-)
lib/strncpy_from_user.c +3 -2
@@ -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
lib/strnlen_user.c +2 -2
@@ -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;
tip-bot for Peter Zijlstra
merge bot[tip:core/objtool] mm/uaccess: Use 'unsigned long' to placate UBSAN warnings on older GCC versions
mm/uaccess: Use 'unsigned long' to placate UBSAN warnings on older GCC versions
Commit-ID: 29da93fea3ea39ab9b12270cc6be1b70ef201c9e Gitweb: https://git.kernel.org/tip/29da93fea3ea39ab9b12270cc6be1b70ef201c9e Author: Peter Zijlstra <[email protected]> AuthorDate: Wed, 24 Apr 2019 09:19:25 +0200 Committer: Ingo Molnar <[email protected]> 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.
--- lib/strncpy_from_user.c | 5 +++-- lib/strnlen_user.c | 4 ++-- 2 files changed, 5 insertions(+), 4 deletions(-)
lib/strncpy_from_user.c +3 -2
@@ -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
lib/strnlen_user.c +2 -2
@@ -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;