On Thu, 22 Jun 2017 00:08:37 +0530 "Naveen N. Rao" <naveen.n....@linux.vnet.ibm.com> wrote:
> Currently, we assume that the function pointer we receive in > ppc_function_entry() points to a function descriptor. However, this is > not always the case. In particular, assembly symbols without the right > annotation do not have an associated function descriptor. Some of these > symbols are added to the kprobe blacklist using _ASM_NOKPROBE_SYMBOL(). > When such addresses are subsequently processed through > arch_deref_entry_point() in populate_kprobe_blacklist(), we see the > below errors during bootup: > [ 0.663963] Failed to find blacklist at 7d9b02a648029b6c > [ 0.663970] Failed to find blacklist at a14d03d0394a0001 > [ 0.663972] Failed to find blacklist at 7d5302a6f94d0388 > [ 0.663973] Failed to find blacklist at 48027d11e8610178 > [ 0.663974] Failed to find blacklist at f8010070f8410080 > [ 0.663976] Failed to find blacklist at 386100704801f89d > [ 0.663977] Failed to find blacklist at 7d5302a6f94d00b0 > > Fix this by checking if the address in the function descriptor is > actually a valid kernel address. In the case of assembly symbols, this > will almost always fail as this ends up being powerpc instructions. In > that case, return pointer to the address we received, rather than the > dereferenced value. > > Signed-off-by: Naveen N. Rao <naveen.n....@linux.vnet.ibm.com> > --- > arch/powerpc/include/asm/code-patching.h | 10 +++++++++- > 1 file changed, 9 insertions(+), 1 deletion(-) > > diff --git a/arch/powerpc/include/asm/code-patching.h > b/arch/powerpc/include/asm/code-patching.h > index abef812de7f8..ec54050be585 100644 > --- a/arch/powerpc/include/asm/code-patching.h > +++ b/arch/powerpc/include/asm/code-patching.h > @@ -83,8 +83,16 @@ static inline unsigned long ppc_function_entry(void *func) > * On PPC64 ABIv1 the function pointer actually points to the > * function's descriptor. The first entry in the descriptor is the > * address of the function text. > + * > + * However, we may have received a pointer to an assembly symbol > + * that may not be a function descriptor. Validate that the entry > + * points to a valid kernel address and if not, return the pointer > + * we received as is. > */ > - return ((func_descr_t *)func)->entry; > + if (kernel_text_address(((func_descr_t *)func)->entry)) > + return ((func_descr_t *)func)->entry; > + else > + return (unsigned long)func; What if "func" is a text section label (bare asm function)? Won't func->entry load the random instruction located there and compare it with a kernel address? I don't know too much about the v1 ABI, but should we check for func belonging in the .opd section first and base the check on that? Alternatively I if "func" is in the kernel text address, we can recognize it's not in the .opd section... right? Thanks, Nick
