[PATCH v5] powerpc/uprobes: Validation for prefixed instruction

[PATCH v5] powerpc/uprobes: Validation for prefixed instruction

[Ravi Bangoria]

As per ISA 3.1, prefixed instruction should not cross 64-byte
boundary. So don't allow Uprobe on such prefixed instruction.

There are two ways probed instruction is changed in mapped pages.
First, when Uprobe is activated, it searches for all the relevant
pages and replace instruction in them. In this case, if that probe
is on the 64-byte unaligned prefixed instruction, error out
directly. Second, when Uprobe is already active and user maps a
relevant page via mmap(), instruction is replaced via mmap() code
path. But because Uprobe is invalid, entire mmap() operation can
not be stopped. In this case just print an error and continue.

Signed-off-by: Ravi Bangoria <ravi.bangoria@linux.ibm.com>
Acked-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
Acked-by: Sandipan Das <sandipan@linux.ibm.com>
---
v4: https://lore.kernel.org/r/20210305115433.140769-1-ravi.bangoria@linux.ibm.com
v4->v5:
  - Replace SZ_ macros with numbers

 arch/powerpc/kernel/uprobes.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/arch/powerpc/kernel/uprobes.c b/arch/powerpc/kernel/uprobes.c
index e8a63713e655..186f69b11e94 100644
--- a/arch/powerpc/kernel/uprobes.c
+++ b/arch/powerpc/kernel/uprobes.c
@@ -41,6 +41,13 @@ int arch_uprobe_analyze_insn(struct arch_uprobe *auprobe,
 	if (addr & 0x03)
 		return -EINVAL;
 
+	if (cpu_has_feature(CPU_FTR_ARCH_31) &&
+	    ppc_inst_prefixed(auprobe->insn) &&
+	    (addr & 0x3f) == 60) {
+		pr_info_ratelimited("Cannot register a uprobe on 64 byte unaligned prefixed instruction\n");
+		return -EINVAL;
+	}
+
 	return 0;
 }
 
-- 
2.27.0

Re: [PATCH v5] powerpc/uprobes: Validation for prefixed instruction

[Michael Ellerman]

On Thu, 11 Mar 2021 14:45:38 +0530, Ravi Bangoria wrote:
> As per ISA 3.1, prefixed instruction should not cross 64-byte
> boundary. So don't allow Uprobe on such prefixed instruction.
> 
> There are two ways probed instruction is changed in mapped pages.
> First, when Uprobe is activated, it searches for all the relevant
> pages and replace instruction in them. In this case, if that probe
> is on the 64-byte unaligned prefixed instruction, error out
> directly. Second, when Uprobe is already active and user maps a
> relevant page via mmap(), instruction is replaced via mmap() code
> path. But because Uprobe is invalid, entire mmap() operation can
> not be stopped. In this case just print an error and continue.

Applied to powerpc/next.

[1/1] powerpc/uprobes: Validation for prefixed instruction
      https://git.kernel.org/powerpc/c/d943bc742a6aabc578b6b62a713ceedf8bf16623

cheers