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| author |   Nick Desaulniers <ndesaulniers@google.com> | 2020-03-26 11:37:06 -0700 |
|---|---|---|
| committer |   Ingo Molnar <mingo@kernel.org> | 2020-04-22 10:53:49 +0200 |
| commit | e378fa17d3fac5b118381923abd2636f45a98c6e (patch) | |
| tree | e5ee259c0a01130777ec0a27caaf993981d4da38 /tools/objtool | |
| parent | objtool: Split out arch-specific CFI definitions (diff) | |
| download | linux-dev-e378fa17d3fac5b118381923abd2636f45a98c6e.tar.xz linux-dev-e378fa17d3fac5b118381923abd2636f45a98c6e.zip | |
objtool: Documentation: document UACCESS warnings
Compiling with Clang and CONFIG_KASAN=y was exposing a few warnings:
call to memset() with UACCESS enabled
Document how to fix these for future travelers.
Link: https://github.com/ClangBuiltLinux/linux/issues/876
Suggested-by: Kamalesh Babulal <kamalesh@linux.vnet.ibm.com>
Suggested-by: Matt Helsley <mhelsley@vmware.com>
Suggested-by: Peter Zijlstra <peterz@infradead.org>
Suggested-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'tools/objtool')
| -rw-r--r-- | tools/objtool/Documentation/stack-validation.txt | 26 |
1 files changed, 26 insertions, 0 deletions
diff --git a/tools/objtool/Documentation/stack-validation.txt b/tools/objtool/Documentation/stack-validation.txt index de094670050b..faa47c3aafae 100644 --- a/tools/objtool/Documentation/stack-validation.txt +++ b/tools/objtool/Documentation/stack-validation.txt @@ -289,6 +289,32 @@ they mean, and suggestions for how to fix them. might be corrupt due to a gcc bug. For more details, see: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70646 +9. file.o: warning: objtool: funcA() call to funcB() with UACCESS enabled + + This means that an unexpected call to a non-whitelisted function exists + outside of arch-specific guards. + X86: SMAP (stac/clac): __uaccess_begin()/__uaccess_end() + ARM: PAN: uaccess_enable()/uaccess_disable() + + These functions should be called to denote a minimal critical section around + access to __user variables. See also: https://lwn.net/Articles/517475/ + + The intention of the warning is to prevent calls to funcB() from eventually + calling schedule(), potentially leaking the AC flags state, and not + restoring them correctly. + + It also helps verify that there are no unexpected calls to funcB() which may + access user space pages with protections against doing so disabled. + + To fix, either: + 1) remove explicit calls to funcB() from funcA(). + 2) add the correct guards before and after calls to low level functions like + __get_user_size()/__put_user_size(). + 3) add funcB to uaccess_safe_builtin whitelist in tools/objtool/check.c, if + funcB obviously does not call schedule(), and is marked notrace (since + function tracing inserts additional calls, which is not obvious from the + sources). + If the error doesn't seem to make sense, it could be a bug in objtool. Feel free to ask the objtool maintainer for help. |