This is a note to let you know that I've just added the patch titled powerpc/book3s64: Fix branching to OOL handlers in relocatable kernel to the 4.5-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: powerpc-book3s64-fix-branching-to-ool-handlers-in-relocatable-kernel.patch and it can be found in the queue-4.5 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. >From 8ed8ab40047a570fdd8043a40c104a57248dd3fd Mon Sep 17 00:00:00 2001 From: Hari Bathini <hbathini@xxxxxxxxxxxxxxxxxx> Date: Fri, 15 Apr 2016 22:48:02 +1000 Subject: powerpc/book3s64: Fix branching to OOL handlers in relocatable kernel From: Hari Bathini <hbathini@xxxxxxxxxxxxxxxxxx> commit 8ed8ab40047a570fdd8043a40c104a57248dd3fd upstream. Some of the interrupt vectors on 64-bit POWER server processors are only 32 bytes long (8 instructions), which is not enough for the full first-level interrupt handler. For these we need to branch to an out-of-line (OOL) handler. But when we are running a relocatable kernel, interrupt vectors till __end_interrupts marker are copied down to real address 0x100. So, branching to labels (ie. OOL handlers) outside this section must be handled differently (see LOAD_HANDLER()), considering relocatable kernel, which would need at least 4 instructions. However, branching from interrupt vector means that we corrupt the CFAR (come-from address register) on POWER7 and later processors as mentioned in commit 1707dd16. So, EXCEPTION_PROLOG_0 (6 instructions) that contains the part up to the point where the CFAR is saved in the PACA should be part of the short interrupt vectors before we branch out to OOL handlers. But as mentioned already, there are interrupt vectors on 64-bit POWER server processors that are only 32 bytes long (like vectors 0x4f00, 0x4f20, etc.), which cannot accomodate the above two cases at the same time owing to space constraint. Currently, in these interrupt vectors, we simply branch out to OOL handlers, without using LOAD_HANDLER(), which leaves us vulnerable when running a relocatable kernel (eg. kdump case). While this has been the case for sometime now and kdump is used widely, we were fortunate not to see any problems so far, for three reasons: 1. In almost all cases, production kernel (relocatable) is used for kdump as well, which would mean that crashed kernel's OOL handler would be at the same place where we end up branching to, from short interrupt vector of kdump kernel. 2. Also, OOL handler was unlikely the reason for crash in almost all the kdump scenarios, which meant we had a sane OOL handler from crashed kernel that we branched to. 3. On most 64-bit POWER server processors, page size is large enough that marking interrupt vector code as executable (see commit 429d2e83) leads to marking OOL handler code from crashed kernel, that sits right below interrupt vector code from kdump kernel, as executable as well. Let us fix this by moving the __end_interrupts marker down past OOL handlers to make sure that we also copy OOL handlers to real address 0x100 when running a relocatable kernel. This fix has been tested successfully in kdump scenario, on an LPAR with 4K page size by using different default/production kernel and kdump kernel. Also tested by manually corrupting the OOL handlers in the first kernel and then kdump'ing, and then causing the OOL handlers to fire - mpe. Fixes: c1fb6816fb1b ("powerpc: Add relocation on exception vector handlers") Signed-off-by: Hari Bathini <hbathini@xxxxxxxxxxxxxxxxxx> Signed-off-by: Mahesh Salgaonkar <mahesh@xxxxxxxxxxxxxxxxxx> Signed-off-by: Michael Ellerman <mpe@xxxxxxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- arch/powerpc/kernel/exceptions-64s.S | 16 +++++++++++----- 1 file changed, 11 insertions(+), 5 deletions(-) --- a/arch/powerpc/kernel/exceptions-64s.S +++ b/arch/powerpc/kernel/exceptions-64s.S @@ -953,11 +953,6 @@ hv_facility_unavailable_relon_trampoline #endif STD_RELON_EXCEPTION_PSERIES(0x5700, 0x1700, altivec_assist) - /* Other future vectors */ - .align 7 - .globl __end_interrupts -__end_interrupts: - .align 7 system_call_entry: b system_call_common @@ -1244,6 +1239,17 @@ __end_handlers: STD_RELON_EXCEPTION_PSERIES_OOL(0xf60, facility_unavailable) STD_RELON_EXCEPTION_HV_OOL(0xf80, hv_facility_unavailable) + /* + * The __end_interrupts marker must be past the out-of-line (OOL) + * handlers, so that they are copied to real address 0x100 when running + * a relocatable kernel. This ensures they can be reached from the short + * trampoline handlers (like 0x4f00, 0x4f20, etc.) which branch + * directly, without using LOAD_HANDLER(). + */ + .align 7 + .globl __end_interrupts +__end_interrupts: + #if defined(CONFIG_PPC_PSERIES) || defined(CONFIG_PPC_POWERNV) /* * Data area reserved for FWNMI option. Patches currently in stable-queue which might be from hbathini@xxxxxxxxxxxxxxxxxx are queue-4.5/powerpc-book3s64-fix-branching-to-ool-handlers-in-relocatable-kernel.patch -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html