aboutsummaryrefslogtreecommitdiff
path: root/mm/maccess.c
diff options
context:
space:
mode:
authorLinus Torvalds <torvalds@linux-foundation.org>2019-02-25 09:10:51 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2019-02-25 09:10:51 -0800
commit53a41cb7ed381edee91029cdcabe9b3250f43f4d (patch)
tree9c22c265fcde82972e9fa0333ee27e612e3a1491 /mm/maccess.c
parent5908e6b738e3357af42c10e1183753c70a0117a9 (diff)
downloadlinux-stericsson-53a41cb7ed381edee91029cdcabe9b3250f43f4d.tar.gz
Revert "x86/fault: BUG() when uaccess helpers fault on kernel addresses"
This reverts commit 9da3f2b74054406f87dff7101a569217ffceb29b. It was well-intentioned, but wrong. Overriding the exception tables for instructions for random reasons is just wrong, and that is what the new code did. It caused problems for tracing, and it caused problems for strncpy_from_user(), because the new checks made perfectly valid use cases break, rather than catch things that did bad things. Unchecked user space accesses are a problem, but that's not a reason to add invalid checks that then people have to work around with silly flags (in this case, that 'kernel_uaccess_faults_ok' flag, which is just an odd way to say "this commit was wrong" and was sprinked into random places to hide the wrongness). The real fix to unchecked user space accesses is to get rid of the special "let's not check __get_user() and __put_user() at all" logic. Make __{get|put}_user() be just aliases to the regular {get|put}_user() functions, and make it impossible to access user space without having the proper checks in places. The raison d'ĂȘtre of the special double-underscore versions used to be that the range check was expensive, and if you did multiple user accesses, you'd do the range check up front (like the signal frame handling code, for example). But SMAP (on x86) and PAN (on ARM) have made that optimization pointless, because the _real_ expense is the "set CPU flag to allow user space access". Do let's not break the valid cases to catch invalid cases that shouldn't even exist. Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Kees Cook <keescook@chromium.org> Cc: Tobin C. Harding <tobin@kernel.org> Cc: Borislav Petkov <bp@alien8.de> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Andy Lutomirski <luto@kernel.org> Cc: Jann Horn <jannh@google.com> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm/maccess.c')
-rw-r--r--mm/maccess.c6
1 files changed, 0 insertions, 6 deletions
diff --git a/mm/maccess.c b/mm/maccess.c
index f3416632e5a4..ec00be51a24f 100644
--- a/mm/maccess.c
+++ b/mm/maccess.c
@@ -30,10 +30,8 @@ long __probe_kernel_read(void *dst, const void *src, size_t size)
set_fs(KERNEL_DS);
pagefault_disable();
- current->kernel_uaccess_faults_ok++;
ret = __copy_from_user_inatomic(dst,
(__force const void __user *)src, size);
- current->kernel_uaccess_faults_ok--;
pagefault_enable();
set_fs(old_fs);
@@ -60,9 +58,7 @@ long __probe_kernel_write(void *dst, const void *src, size_t size)
set_fs(KERNEL_DS);
pagefault_disable();
- current->kernel_uaccess_faults_ok++;
ret = __copy_to_user_inatomic((__force void __user *)dst, src, size);
- current->kernel_uaccess_faults_ok--;
pagefault_enable();
set_fs(old_fs);
@@ -98,13 +94,11 @@ long strncpy_from_unsafe(char *dst, const void *unsafe_addr, long count)
set_fs(KERNEL_DS);
pagefault_disable();
- current->kernel_uaccess_faults_ok++;
do {
ret = __get_user(*dst++, (const char __user __force *)src++);
} while (dst[-1] && ret == 0 && src - unsafe_addr < count);
- current->kernel_uaccess_faults_ok--;
dst[-1] = '\0';
pagefault_enable();
set_fs(old_fs);