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-rw-r--r--tools/objtool/Documentation/stack-validation.txt41
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diff --git a/tools/objtool/Documentation/stack-validation.txt b/tools/objtool/Documentation/stack-validation.txt
index de094670050b..0542e46c7552 100644
--- a/tools/objtool/Documentation/stack-validation.txt
+++ b/tools/objtool/Documentation/stack-validation.txt
@@ -289,6 +289,47 @@ 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).
+
+10. file.o: warning: func()+0x5c: alternative modifies stack
+
+ This means that an alternative includes instructions that modify the
+ stack. The problem is that there is only one ORC unwind table, this means
+ that the ORC unwind entries must be valid for each of the alternatives.
+ The easiest way to enforce this is to ensure alternatives do not contain
+ any ORC entries, which in turn implies the above constraint.
+
+11. file.o: warning: unannotated intra-function call
+
+ This warning means that a direct call is done to a destination which
+ is not at the beginning of a function. If this is a legit call, you
+ can remove this warning by putting the ANNOTATE_INTRA_FUNCTION_CALL
+ directive right before the call.
+
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.