[PATCH v1] powerpc/64s: Fix scv implicit soft-mask table for relocated kernels

[PATCH v1] powerpc/64s: Fix scv implicit soft-mask table for relocated kernels

[Nicholas Piggin]

The implict soft-mask table addresses get relocated if they use a
relative symbol like a label. This is right for code that runs relocated
but not for unrelocated. The scv interrupt vectors run unrelocated, so
absolute addresses are required for their soft-mask table entry.

This fixes crashing with relocated kernels, usually an asynchronous
interrupt hitting in the scv handler, then hitting the trap that checks
whether r1 is in userspace.

Cc: Hari Bathini <hbathini@linux.ibm.com>
Fixes: 325678fd0522 ("powerpc/64s: add a table of implicit soft-masked addresses")
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
---
 arch/powerpc/kernel/exceptions-64s.S | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/arch/powerpc/kernel/exceptions-64s.S b/arch/powerpc/kernel/exceptions-64s.S
index 4aec59a77d4c..37859e62a8dc 100644
--- a/arch/powerpc/kernel/exceptions-64s.S
+++ b/arch/powerpc/kernel/exceptions-64s.S
@@ -812,7 +812,6 @@ __start_interrupts:
  * syscall register convention is in Documentation/powerpc/syscall64-abi.rst
  */
 EXC_VIRT_BEGIN(system_call_vectored, 0x3000, 0x1000)
-1:
 	/* SCV 0 */
 	mr	r9,r13
 	GET_PACA(r13)
@@ -842,10 +841,12 @@ EXC_VIRT_BEGIN(system_call_vectored, 0x3000, 0x1000)
 	b	system_call_vectored_sigill
 #endif
 	.endr
-2:
 EXC_VIRT_END(system_call_vectored, 0x3000, 0x1000)
 
-SOFT_MASK_TABLE(1b, 2b) // Treat scv vectors as soft-masked, see comment above.
+// Treat scv vectors as soft-masked, see comment above.
+// Use absolute values rather than labels here, so they don't get relocated,
+// because this code runs unrelocated.
+SOFT_MASK_TABLE(0xc000000000003000, 0xc000000000004000)
 
 #ifdef CONFIG_RELOCATABLE
 TRAMP_VIRT_BEGIN(system_call_vectored_tramp)
-- 
2.23.0

Re: [PATCH v1] powerpc/64s: Fix scv implicit soft-mask table for relocated kernels

[Michael Ellerman]

On Fri, 20 Aug 2021 20:34:31 +1000, Nicholas Piggin wrote:
> The implict soft-mask table addresses get relocated if they use a
> relative symbol like a label. This is right for code that runs relocated
> but not for unrelocated. The scv interrupt vectors run unrelocated, so
> absolute addresses are required for their soft-mask table entry.
> 
> This fixes crashing with relocated kernels, usually an asynchronous
> interrupt hitting in the scv handler, then hitting the trap that checks
> whether r1 is in userspace.
> 
> [...]

Applied to powerpc/fixes.

[1/1] powerpc/64s: Fix scv implicit soft-mask table for relocated kernels
      https://git.kernel.org/powerpc/c/787c70f2f9990b5a197320152d2fc32cd8a6ad1a

cheers