With CONFIG_CFI_CLANG and ThinLTO, Clang appends a hash to the names
of all static functions not marked __used. This can break userspace
tools that don't expect the function name to change, so strip out the
hash from the output.
Suggested-by: Jack Pham <[email protected]>
Signed-off-by: Sami Tolvanen <[email protected]>
Reviewed-by: Kees Cook <[email protected]>
---
kernel/kallsyms.c | 54 ++++++++++++++++++++++++++++++++++++++++++-----
1 file changed, 49 insertions(+), 5 deletions(-)
diff --git a/kernel/kallsyms.c b/kernel/kallsyms.c
index 8043a90aa50e..17d3a704bafa 100644
--- a/kernel/kallsyms.c
+++ b/kernel/kallsyms.c
@@ -161,6 +161,26 @@ static unsigned long kallsyms_sym_address(int idx)
return kallsyms_relative_base - 1 - kallsyms_offsets[idx];
}
+#if defined(CONFIG_CFI_CLANG) && defined(CONFIG_LTO_CLANG_THIN)
+/*
+ * LLVM appends a hash to static function names when ThinLTO and CFI are
+ * both enabled, which causes confusion and potentially breaks user space
+ * tools, so we will strip the postfix from expanded symbol names.
+ */
+static inline char *cleanup_symbol_name(char *s)
+{
+ char *res = NULL;
+
+ res = strrchr(s, '$');
+ if (res)
+ *res = '\0';
+
+ return res;
+}
+#else
+static inline char *cleanup_symbol_name(char *s) { return NULL; }
+#endif
+
/* Lookup the address for this symbol. Returns 0 if not found. */
unsigned long kallsyms_lookup_name(const char *name)
{
@@ -173,6 +193,9 @@ unsigned long kallsyms_lookup_name(const char *name)
if (strcmp(namebuf, name) == 0)
return kallsyms_sym_address(i);
+
+ if (cleanup_symbol_name(namebuf) && strcmp(namebuf, name) == 0)
+ return kallsyms_sym_address(i);
}
return module_kallsyms_lookup_name(name);
}
@@ -303,7 +326,9 @@ const char *kallsyms_lookup(unsigned long addr,
namebuf, KSYM_NAME_LEN);
if (modname)
*modname = NULL;
- return namebuf;
+
+ ret = namebuf;
+ goto found;
}
/* See if it's in a module or a BPF JITed image. */
@@ -316,11 +341,16 @@ const char *kallsyms_lookup(unsigned long addr,
if (!ret)
ret = ftrace_mod_address_lookup(addr, symbolsize,
offset, modname, namebuf);
+
+found:
+ cleanup_symbol_name(namebuf);
return ret;
}
int lookup_symbol_name(unsigned long addr, char *symname)
{
+ int res;
+
symname[0] = '\0';
symname[KSYM_NAME_LEN - 1] = '\0';
@@ -331,15 +361,23 @@ int lookup_symbol_name(unsigned long addr, char *symname)
/* Grab name */
kallsyms_expand_symbol(get_symbol_offset(pos),
symname, KSYM_NAME_LEN);
- return 0;
+ goto found;
}
/* See if it's in a module. */
- return lookup_module_symbol_name(addr, symname);
+ res = lookup_module_symbol_name(addr, symname);
+ if (res)
+ return res;
+
+found:
+ cleanup_symbol_name(symname);
+ return 0;
}
int lookup_symbol_attrs(unsigned long addr, unsigned long *size,
unsigned long *offset, char *modname, char *name)
{
+ int res;
+
name[0] = '\0';
name[KSYM_NAME_LEN - 1] = '\0';
@@ -351,10 +389,16 @@ int lookup_symbol_attrs(unsigned long addr, unsigned long *size,
kallsyms_expand_symbol(get_symbol_offset(pos),
name, KSYM_NAME_LEN);
modname[0] = '\0';
- return 0;
+ goto found;
}
/* See if it's in a module. */
- return lookup_module_symbol_attrs(addr, size, offset, modname, name);
+ res = lookup_module_symbol_attrs(addr, size, offset, modname, name);
+ if (res)
+ return res;
+
+found:
+ cleanup_symbol_name(name);
+ return 0;
}
/* Look up a kernel symbol and return it in a text buffer. */
--
2.31.0.291.g576ba9dcdaf-goog
On Thu, Mar 18, 2021 at 10:11 AM Sami Tolvanen <[email protected]> wrote:
>
> With CONFIG_CFI_CLANG and ThinLTO, Clang appends a hash to the names
> of all static functions not marked __used. This can break userspace
> tools that don't expect the function name to change, so strip out the
> hash from the output.
>
> Suggested-by: Jack Pham <[email protected]>
> Signed-off-by: Sami Tolvanen <[email protected]>
> Reviewed-by: Kees Cook <[email protected]>
> ---
> kernel/kallsyms.c | 54 ++++++++++++++++++++++++++++++++++++++++++-----
> 1 file changed, 49 insertions(+), 5 deletions(-)
>
> diff --git a/kernel/kallsyms.c b/kernel/kallsyms.c
> index 8043a90aa50e..17d3a704bafa 100644
> --- a/kernel/kallsyms.c
> +++ b/kernel/kallsyms.c
> @@ -161,6 +161,26 @@ static unsigned long kallsyms_sym_address(int idx)
> return kallsyms_relative_base - 1 - kallsyms_offsets[idx];
> }
>
> +#if defined(CONFIG_CFI_CLANG) && defined(CONFIG_LTO_CLANG_THIN)
> +/*
> + * LLVM appends a hash to static function names when ThinLTO and CFI are
> + * both enabled, which causes confusion and potentially breaks user space
Might be nice to add an example, something along the lines of:
ie. foo() becomes foo$asfdasdfasdfasdf()
> + * tools, so we will strip the postfix from expanded symbol names.
s/postfix/suffix/ ?
> + */
> +static inline char *cleanup_symbol_name(char *s)
> +{
> + char *res = NULL;
> +
> + res = strrchr(s, '$');
> + if (res)
> + *res = '\0';
> +
> + return res;
> +}
> +#else
> +static inline char *cleanup_symbol_name(char *s) { return NULL; }
> +#endif
Might be nicer to return a `bool` and have the larger definition
`return res != NULL`). Not sure what a caller would do with `res` if
it was not `NULL`?
> +
> /* Lookup the address for this symbol. Returns 0 if not found. */
> unsigned long kallsyms_lookup_name(const char *name)
> {
> @@ -173,6 +193,9 @@ unsigned long kallsyms_lookup_name(const char *name)
>
> if (strcmp(namebuf, name) == 0)
> return kallsyms_sym_address(i);
> +
> + if (cleanup_symbol_name(namebuf) && strcmp(namebuf, name) == 0)
> + return kallsyms_sym_address(i);
> }
> return module_kallsyms_lookup_name(name);
> }
> @@ -303,7 +326,9 @@ const char *kallsyms_lookup(unsigned long addr,
> namebuf, KSYM_NAME_LEN);
> if (modname)
> *modname = NULL;
> - return namebuf;
> +
> + ret = namebuf;
> + goto found;
> }
>
> /* See if it's in a module or a BPF JITed image. */
> @@ -316,11 +341,16 @@ const char *kallsyms_lookup(unsigned long addr,
> if (!ret)
> ret = ftrace_mod_address_lookup(addr, symbolsize,
> offset, modname, namebuf);
> +
> +found:
> + cleanup_symbol_name(namebuf);
> return ret;
> }
>
> int lookup_symbol_name(unsigned long addr, char *symname)
> {
> + int res;
> +
> symname[0] = '\0';
> symname[KSYM_NAME_LEN - 1] = '\0';
>
> @@ -331,15 +361,23 @@ int lookup_symbol_name(unsigned long addr, char *symname)
> /* Grab name */
> kallsyms_expand_symbol(get_symbol_offset(pos),
> symname, KSYM_NAME_LEN);
> - return 0;
> + goto found;
> }
> /* See if it's in a module. */
> - return lookup_module_symbol_name(addr, symname);
> + res = lookup_module_symbol_name(addr, symname);
> + if (res)
> + return res;
> +
> +found:
> + cleanup_symbol_name(symname);
> + return 0;
> }
>
> int lookup_symbol_attrs(unsigned long addr, unsigned long *size,
> unsigned long *offset, char *modname, char *name)
> {
> + int res;
> +
> name[0] = '\0';
> name[KSYM_NAME_LEN - 1] = '\0';
>
> @@ -351,10 +389,16 @@ int lookup_symbol_attrs(unsigned long addr, unsigned long *size,
> kallsyms_expand_symbol(get_symbol_offset(pos),
> name, KSYM_NAME_LEN);
> modname[0] = '\0';
> - return 0;
> + goto found;
> }
> /* See if it's in a module. */
> - return lookup_module_symbol_attrs(addr, size, offset, modname, name);
> + res = lookup_module_symbol_attrs(addr, size, offset, modname, name);
> + if (res)
> + return res;
> +
> +found:
> + cleanup_symbol_name(name);
> + return 0;
> }
>
> /* Look up a kernel symbol and return it in a text buffer. */
> --
> 2.31.0.291.g576ba9dcdaf-goog
>
--
Thanks,
~Nick Desaulniers
On Thu, Mar 18, 2021 at 12:00 PM Nick Desaulniers
<[email protected]> wrote:
>
> On Thu, Mar 18, 2021 at 10:11 AM Sami Tolvanen <[email protected]> wrote:
> >
> > With CONFIG_CFI_CLANG and ThinLTO, Clang appends a hash to the names
> > of all static functions not marked __used. This can break userspace
> > tools that don't expect the function name to change, so strip out the
> > hash from the output.
> >
> > Suggested-by: Jack Pham <[email protected]>
> > Signed-off-by: Sami Tolvanen <[email protected]>
> > Reviewed-by: Kees Cook <[email protected]>
> > ---
> > kernel/kallsyms.c | 54 ++++++++++++++++++++++++++++++++++++++++++-----
> > 1 file changed, 49 insertions(+), 5 deletions(-)
> >
> > diff --git a/kernel/kallsyms.c b/kernel/kallsyms.c
> > index 8043a90aa50e..17d3a704bafa 100644
> > --- a/kernel/kallsyms.c
> > +++ b/kernel/kallsyms.c
> > @@ -161,6 +161,26 @@ static unsigned long kallsyms_sym_address(int idx)
> > return kallsyms_relative_base - 1 - kallsyms_offsets[idx];
> > }
> >
> > +#if defined(CONFIG_CFI_CLANG) && defined(CONFIG_LTO_CLANG_THIN)
> > +/*
> > + * LLVM appends a hash to static function names when ThinLTO and CFI are
> > + * both enabled, which causes confusion and potentially breaks user space
>
> Might be nice to add an example, something along the lines of:
> ie. foo() becomes foo$asfdasdfasdfasdf()
Agreed, I'll update the comment in v3.
>
> > + * tools, so we will strip the postfix from expanded symbol names.
>
> s/postfix/suffix/ ?
Ack.
>
> > + */
> > +static inline char *cleanup_symbol_name(char *s)
> > +{
> > + char *res = NULL;
> > +
> > + res = strrchr(s, '$');
> > + if (res)
> > + *res = '\0';
> > +
> > + return res;
> > +}
> > +#else
> > +static inline char *cleanup_symbol_name(char *s) { return NULL; }
> > +#endif
>
> Might be nicer to return a `bool` and have the larger definition
> `return res != NULL`). Not sure what a caller would do with `res` if
> it was not `NULL`?
Sure, I'll change this to bool.
Sami