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Aligning address to page boundary allows flush_tlb_kernel_range()
to know it's a single page flush and use tlbie instead of tlbia.
On 603 we now have the following code in first leg of
change_page_attr():
2c: 55 29 00 3c rlwinm r9,r9,0,0,30
30: 91 23 00 00 stw r9,0(r3)
34: 7c 00 22 64 tlbie r4,r0
38: 7c 00 04 ac hwsync
3c: 38 60 00 00 li r3,0
40: 4e 80 00 20 blr
Before we had:
28: 55 29 00 3c rlwinm r9,r9,0,0,30
2c: 91 23 00 00 stw r9,0(r3)
30: 54 89 00 26 rlwinm r9,r4,0,0,19
34: 38 84 10 00 addi r4,r4,4096
38: 7c 89 20 50 subf r4,r9,r4
3c: 28 04 10 00 cmplwi r4,4096
40: 41 81 00 30 bgt 70 <change_page_attr+0x70>
44: 7c 00 4a 64 tlbie r9,r0
48: 7c 00 04 ac hwsync
4c: 38 60 00 00 li r3,0
50: 4e 80 00 20 blr
...
70: 94 21 ff f0 stwu r1,-16(r1)
74: 7c 08 02 a6 mflr r0
78: 90 01 00 14 stw r0,20(r1)
7c: 48 00 00 01 bl 7c <change_page_attr+0x7c>
7c: R_PPC_REL24 _tlbia
80: 80 01 00 14 lwz r0,20(r1)
84: 38 60 00 00 li r3,0
88: 7c 08 03 a6 mtlr r0
8c: 38 21 00 10 addi r1,r1,16
90: 4e 80 00 20 blr
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/6bb118fb2ee89fa3c1f9cf90ed19f88220002cb0.1647877467.git.christophe.leroy@csgroup.eu
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set_memory_attr() was implemented by commit 4d1755b6a762 ("powerpc/mm:
implement set_memory_attr()") because the set_memory_xx() couldn't
be used at that time to modify memory "on the fly" as explained it
the commit.
But set_memory_attr() uses set_pte_at() which leads to warnings when
CONFIG_DEBUG_VM is selected, because set_pte_at() is unexpected for
updating existing page table entries.
The check could be bypassed by using __set_pte_at() instead,
as it was the case before commit c988cfd38e48 ("powerpc/32:
use set_memory_attr()") but since commit 9f7853d7609d ("powerpc/mm:
Fix set_memory_*() against concurrent accesses") it is now possible
to use set_memory_xx() functions to update page table entries
"on the fly" because the update is now atomic.
For DEBUG_PAGEALLOC we need to clear and set back _PAGE_PRESENT.
Add set_memory_np() and set_memory_p() for that.
Replace all uses of set_memory_attr() by the relevant set_memory_xx()
and remove set_memory_attr().
Fixes: c988cfd38e48 ("powerpc/32: use set_memory_attr()")
Cc: stable@vger.kernel.org
Reported-by: Maxime Bizon <mbizon@freebox.fr>
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Tested-by: Maxime Bizon <mbizon@freebox.fr>
Reviewed-by: Russell Currey <ruscur@russell.cc>
Depends-on: 9f7853d7609d ("powerpc/mm: Fix set_memory_*() against concurrent accesses")
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/cda2b44b55c96f9ac69fa92e68c01084ec9495c5.1640344012.git.christophe.leroy@csgroup.eu
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Commit 1f9ad21c3b38 ("powerpc/mm: Implement set_memory() routines")
included a spin_lock() to change_page_attr() in order to
safely perform the three step operations. But then
commit 9f7853d7609d ("powerpc/mm: Fix set_memory_*() against
concurrent accesses") modify it to use pte_update() and do
the operation safely against concurrent access.
In the meantime, Maxime reported some spinlock recursion.
[ 15.351649] BUG: spinlock recursion on CPU#0, kworker/0:2/217
[ 15.357540] lock: init_mm+0x3c/0x420, .magic: dead4ead, .owner: kworker/0:2/217, .owner_cpu: 0
[ 15.366563] CPU: 0 PID: 217 Comm: kworker/0:2 Not tainted 5.15.0+ #523
[ 15.373350] Workqueue: events do_free_init
[ 15.377615] Call Trace:
[ 15.380232] [e4105ac0] [800946a4] do_raw_spin_lock+0xf8/0x120 (unreliable)
[ 15.387340] [e4105ae0] [8001f4ec] change_page_attr+0x40/0x1d4
[ 15.393413] [e4105b10] [801424e0] __apply_to_page_range+0x164/0x310
[ 15.400009] [e4105b60] [80169620] free_pcp_prepare+0x1e4/0x4a0
[ 15.406045] [e4105ba0] [8016c5a0] free_unref_page+0x40/0x2b8
[ 15.411979] [e4105be0] [8018724c] kasan_depopulate_vmalloc_pte+0x6c/0x94
[ 15.418989] [e4105c00] [801424e0] __apply_to_page_range+0x164/0x310
[ 15.425451] [e4105c50] [80187834] kasan_release_vmalloc+0xbc/0x134
[ 15.431898] [e4105c70] [8015f7a8] __purge_vmap_area_lazy+0x4e4/0xdd8
[ 15.438560] [e4105d30] [80160d10] _vm_unmap_aliases.part.0+0x17c/0x24c
[ 15.445283] [e4105d60] [801642d0] __vunmap+0x2f0/0x5c8
[ 15.450684] [e4105db0] [800e32d0] do_free_init+0x68/0x94
[ 15.456181] [e4105dd0] [8005d094] process_one_work+0x4bc/0x7b8
[ 15.462283] [e4105e90] [8005d614] worker_thread+0x284/0x6e8
[ 15.468227] [e4105f00] [8006aaec] kthread+0x1f0/0x210
[ 15.473489] [e4105f40] [80017148] ret_from_kernel_thread+0x14/0x1c
Remove the read / modify / write sequence to make the operation atomic
and remove the spin_lock() in change_page_attr().
To do the operation atomically, we can't use pte modification helpers
anymore. Because all platforms have different combination of bits, it
is not easy to use those bits directly. But all have the
_PAGE_KERNEL_{RO/ROX/RW/RWX} set of flags. All we need it to compare
two sets to know which bits are set or cleared.
For instance, by comparing _PAGE_KERNEL_ROX and _PAGE_KERNEL_RO you
know which bit gets cleared and which bit get set when changing exec
permission.
Reported-by: Maxime Bizon <mbizon@freebox.fr>
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/all/20211212112152.GA27070@sakura/
Link: https://lore.kernel.org/r/43c3c76a1175ae6dc1a3d3b5c3f7ecb48f683eea.1640344012.git.christophe.leroy@csgroup.eu
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Laurent reported that STRICT_MODULE_RWX was causing intermittent crashes
on one of his systems:
kernel tried to execute exec-protected page (c008000004073278) - exploit attempt? (uid: 0)
BUG: Unable to handle kernel instruction fetch
Faulting instruction address: 0xc008000004073278
Oops: Kernel access of bad area, sig: 11 [#1]
LE PAGE_SIZE=64K MMU=Radix SMP NR_CPUS=2048 NUMA pSeries
Modules linked in: drm virtio_console fuse drm_panel_orientation_quirks ...
CPU: 3 PID: 44 Comm: kworker/3:1 Not tainted 5.14.0-rc4+ #12
Workqueue: events control_work_handler [virtio_console]
NIP: c008000004073278 LR: c008000004073278 CTR: c0000000001e9de0
REGS: c00000002e4ef7e0 TRAP: 0400 Not tainted (5.14.0-rc4+)
MSR: 800000004280b033 <SF,VEC,VSX,EE,FP,ME,IR,DR,RI,LE> CR: 24002822 XER: 200400cf
...
NIP fill_queue+0xf0/0x210 [virtio_console]
LR fill_queue+0xf0/0x210 [virtio_console]
Call Trace:
fill_queue+0xb4/0x210 [virtio_console] (unreliable)
add_port+0x1a8/0x470 [virtio_console]
control_work_handler+0xbc/0x1e8 [virtio_console]
process_one_work+0x290/0x590
worker_thread+0x88/0x620
kthread+0x194/0x1a0
ret_from_kernel_thread+0x5c/0x64
Jordan, Fabiano & Murilo were able to reproduce and identify that the
problem is caused by the call to module_enable_ro() in do_init_module(),
which happens after the module's init function has already been called.
Our current implementation of change_page_attr() is not safe against
concurrent accesses, because it invalidates the PTE before flushing the
TLB and then installing the new PTE. That leaves a window in time where
there is no valid PTE for the page, if another CPU tries to access the
page at that time we see something like the fault above.
We can't simply switch to set_pte_at()/flush TLB, because our hash MMU
code doesn't handle a set_pte_at() of a valid PTE. See [1].
But we do have pte_update(), which replaces the old PTE with the new,
meaning there's no window where the PTE is invalid. And the hash MMU
version hash__pte_update() deals with synchronising the hash page table
correctly.
[1]: https://lore.kernel.org/linuxppc-dev/87y318wp9r.fsf@linux.ibm.com/
Fixes: 1f9ad21c3b38 ("powerpc/mm: Implement set_memory() routines")
Reported-by: Laurent Vivier <lvivier@redhat.com>
Reviewed-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Reviewed-by: Murilo Opsfelder Araújo <muriloo@linux.ibm.com>
Tested-by: Laurent Vivier <lvivier@redhat.com>
Signed-off-by: Fabiano Rosas <farosas@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20210818120518.3603172-1-mpe@ellerman.id.au
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In addition to the set_memory_xx() functions which allows to change
the memory attributes of not (yet) used memory regions, implement a
set_memory_attr() function to:
- set the final memory protection after init on currently used
kernel regions.
- enable/disable kernel memory regions in the scope of DEBUG_PAGEALLOC.
Unlike the set_memory_xx() which can act in three step as the regions
are unused, this function must modify 'on the fly' as the kernel is
executing from them. At the moment only PPC32 will use it and changing
page attributes on the fly is not an issue.
Reported-by: kbuild test robot <lkp@intel.com>
[ruscur: cast "data" to unsigned long instead of int]
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Russell Currey <ruscur@russell.cc>
Signed-off-by: Jordan Niethe <jniethe5@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20210609013431.9805-9-jniethe5@gmail.com
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The set_memory_{ro/rw/nx/x}() functions are required for
STRICT_MODULE_RWX, and are generally useful primitives to have. This
implementation is designed to be generic across powerpc's many MMUs.
It's possible that this could be optimised to be faster for specific
MMUs.
This implementation does not handle cases where the caller is attempting
to change the mapping of the page it is executing from, or if another
CPU is concurrently using the page being altered. These cases likely
shouldn't happen, but a more complex implementation with MMU-specific code
could safely handle them.
On hash, the linear mapping is not kept in the linux pagetable, so this
will not change the protection if used on that range. Currently these
functions are not used on the linear map so just WARN for now.
apply_to_existing_page_range() does not work on huge pages so for now
disallow changing the protection of huge pages.
[jpn: - Allow set memory functions to be used without Strict RWX
- Hash: Disallow certain regions
- Have change_page_attr() take function pointers to manipulate ptes
- Radix: Add ptesync after set_pte_at()]
Signed-off-by: Russell Currey <ruscur@russell.cc>
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Jordan Niethe <jniethe5@gmail.com>
Reviewed-by: Daniel Axtens <dja@axtens.net>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20210609013431.9805-2-jniethe5@gmail.com
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