| Message ID | 20210831144114.154-17-alexandr.lobakin@intel.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | Function Granular KASLR | expand |
Hi, On Tue, 31 Aug 2021, Alexander Lobakin wrote: > From: Kristen Carlson Accardi <kristen@linux.intel.com> > > If any type of function granular randomization is enabled, the sympos > algorithm will fail, as it will be impossible to resolve symbols when > there are duplicates using the previous symbol position. > > Override the value of sympos to always be zero if fgkaslr is enabled for > either the core kernel or modules, forcing the algorithm > to require that only unique symbols are allowed to be patched. > > Signed-off-by: Kristen Carlson Accardi <kristen@linux.intel.com> > Signed-off-by: Alexander Lobakin <alexandr.lobakin@intel.com> > --- > kernel/livepatch/core.c | 11 +++++++++++ > 1 file changed, 11 insertions(+) > > diff --git a/kernel/livepatch/core.c b/kernel/livepatch/core.c > index 335d988bd811..852bbfa9da7b 100644 > --- a/kernel/livepatch/core.c > +++ b/kernel/livepatch/core.c > @@ -169,6 +169,17 @@ static int klp_find_object_symbol(const char *objname, const char *name, > else > kallsyms_on_each_symbol(klp_find_callback, &args); > > + /* > + * If any type of function granular randomization is enabled, it > + * will be impossible to resolve symbols when there are duplicates > + * using the previous symbol position (i.e. sympos != 0). Override > + * the value of sympos to always be zero in this case. This will > + * force the algorithm to require that only unique symbols are > + * allowed to be patched. > + */ > + if (IS_ENABLED(CONFIG_FG_KASLR)) > + sympos = 0; > + I ran the live patching tests and no problem occurred, which is great. We do not have a test for old_sympos, which makes the testing less telling, but at least nothing blows up with the section randomization itself. However, I want to reiterate what I wrote for the same patch in v5 series. The above hunk should work, but I wonder if we should make it more explicit. With the change the user will get the error with "unresolvable ambiguity for symbol..." if they specify sympos and the symbol is not unique. It could confuse them. So, how about it making it something like if (IS_ENABLED(CONFIG_FG_KASLR) || IS_ENABLED(CONFIG_MODULE_FG_KASLR)) if (sympos) { pr_err("fgkaslr is enabled, specifying sympos for symbol '%s' in object '%s' does not work.\n", name, objname); *addr = 0; return -EINVAL; } ? (there could be goto to the error out at the end of the function to save copy-pasting). In that case, if sympos is not specified, the user will get the message which matches the reality. If the user specifies it, they will get the error in case of fgkaslr (no matter if the symbol is found or not). What do you think? Miroslav
From: Miroslav Benes <mbenes@suse.cz> Date: Thu, 9 Sep 2021 13:53:35 +0200 (CEST) > Hi, Hi! > On Tue, 31 Aug 2021, Alexander Lobakin wrote: > > > From: Kristen Carlson Accardi <kristen@linux.intel.com> > > > > If any type of function granular randomization is enabled, the sympos > > algorithm will fail, as it will be impossible to resolve symbols when > > there are duplicates using the previous symbol position. > > > > Override the value of sympos to always be zero if fgkaslr is enabled for > > either the core kernel or modules, forcing the algorithm > > to require that only unique symbols are allowed to be patched. > > > > Signed-off-by: Kristen Carlson Accardi <kristen@linux.intel.com> > > Signed-off-by: Alexander Lobakin <alexandr.lobakin@intel.com> > > --- > > kernel/livepatch/core.c | 11 +++++++++++ > > 1 file changed, 11 insertions(+) > > > > diff --git a/kernel/livepatch/core.c b/kernel/livepatch/core.c > > index 335d988bd811..852bbfa9da7b 100644 > > --- a/kernel/livepatch/core.c > > +++ b/kernel/livepatch/core.c > > @@ -169,6 +169,17 @@ static int klp_find_object_symbol(const char *objname, const char *name, > > else > > kallsyms_on_each_symbol(klp_find_callback, &args); > > > > + /* > > + * If any type of function granular randomization is enabled, it > > + * will be impossible to resolve symbols when there are duplicates > > + * using the previous symbol position (i.e. sympos != 0). Override > > + * the value of sympos to always be zero in this case. This will > > + * force the algorithm to require that only unique symbols are > > + * allowed to be patched. > > + */ > > + if (IS_ENABLED(CONFIG_FG_KASLR)) > > + sympos = 0; > > + > > I ran the live patching tests and no problem occurred, which is great. We > do not have a test for old_sympos, which makes the testing less telling, > but at least nothing blows up with the section randomization itself. Great, thanks! > However, I want to reiterate what I wrote for the same patch in v5 > series. > > The above hunk should work, but I wonder if we should make it more > explicit. With the change the user will get the error with "unresolvable > ambiguity for symbol..." if they specify sympos and the symbol is not > unique. It could confuse them. > > So, how about it making it something like > > if (IS_ENABLED(CONFIG_FG_KASLR) || IS_ENABLED(CONFIG_MODULE_FG_KASLR)) > if (sympos) { > pr_err("fgkaslr is enabled, specifying sympos for symbol '%s' in object '%s' does not work.\n", > name, objname); > *addr = 0; > return -EINVAL; > } > > ? (there could be goto to the error out at the end of the function to > save copy-pasting). > > In that case, if sympos is not specified, the user will get the message > which matches the reality. If the user specifies it, they will get the > error in case of fgkaslr (no matter if the symbol is found or not). Not familiar with livepatching unfortunately, hope Kristen and/or Kees will comment on this. Looks fine for me anyways. > What do you think? > > Miroslav Thanks, Al
diff --git a/kernel/livepatch/core.c b/kernel/livepatch/core.c index 335d988bd811..852bbfa9da7b 100644 --- a/kernel/livepatch/core.c +++ b/kernel/livepatch/core.c @@ -169,6 +169,17 @@ static int klp_find_object_symbol(const char *objname, const char *name, else kallsyms_on_each_symbol(klp_find_callback, &args); + /* + * If any type of function granular randomization is enabled, it + * will be impossible to resolve symbols when there are duplicates + * using the previous symbol position (i.e. sympos != 0). Override + * the value of sympos to always be zero in this case. This will + * force the algorithm to require that only unique symbols are + * allowed to be patched. + */ + if (IS_ENABLED(CONFIG_FG_KASLR)) + sympos = 0; + /* * Ensure an address was found. If sympos is 0, ensure symbol is unique; * otherwise ensure the symbol position count matches sympos.