From: "Naveen N. Rao" naveen.n.rao@linux.vnet.ibm.com
[ Upstream commit 83e840c770f2c578bbbff478d62a4403c073b438 ]
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 function pointer we receive in ppc_function_entry() already points to kernel text. If so, we just return it as is. If not, we assume that this is a function descriptor and proceed to dereference it.
Suggested-by: Nicholas Piggin npiggin@gmail.com Reviewed-by: Nicholas Piggin npiggin@gmail.com Signed-off-by: Naveen N. Rao naveen.n.rao@linux.vnet.ibm.com Signed-off-by: Michael Ellerman mpe@ellerman.id.au Signed-off-by: Sasha Levin alexander.levin@microsoft.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 b4ab1f497335..a96e4ad380d1 100644 --- a/arch/powerpc/include/asm/code-patching.h +++ b/arch/powerpc/include/asm/code-patching.h @@ -80,8 +80,16 @@ 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 also receive pointer to an assembly symbol. To + * detect that, we first check if the function pointer we receive + * already points to kernel/module text and we only dereference it + * if it doesn't. */ - return ((func_descr_t *)func)->entry; + if (kernel_text_address((unsigned long)func)) + return (unsigned long)func; + else + return ((func_descr_t *)func)->entry; #else return (unsigned long)func; #endif