On Thu, Jun 16, 2022 at 04:11:34PM +0000, Quentin Perret wrote:
> Commit a7259df76702 ("memblock: make memblock_find_in_range method
> private") changed the API using which memory is reserved for the pKVM
> hypervisor. However, it seems that memblock_phys_alloc() differs
> from the original API in terms of kmemleak semantics -- the old one
> excluded the reserved regions from kmemleak scans when the new one
> doesn't seem to. Unfortunately, when protected KVM is enabled, all
I'd rather say that memblock_find_in_range() didn't inform kmemleak about
the reserved regions, while memblock_phys_alloc() does.
> kernel accesses to pKVM-private memory result in a fatal exception,
> which can now happen because of kmemleak scans:
>
> $ echo scan > /sys/kernel/debug/kmemleak
> [ 34.991354] kvm [304]: nVHE hyp BUG at: [<ffff800008fa3750>] __kvm_nvhe_handle_host_mem_abort+0x270/0x290!
> [ 34.991580] kvm [304]: Hyp Offset: 0xfffe8be807e00000
> [ 34.991813] Kernel panic - not syncing: HYP panic:
> [ 34.991813] PS:600003c9 PC:0000f418011a3750 ESR:00000000f2000800
> [ 34.991813] FAR:ffff000439200000 HPFAR:0000000004792000 PAR:0000000000000000
> [ 34.991813] VCPU:0000000000000000
> [ 34.993660] CPU: 0 PID: 304 Comm: bash Not tainted 5.19.0-rc2 #102
> [ 34.994059] Hardware name: linux,dummy-virt (DT)
> [ 34.994452] Call trace:
> [ 34.994641] dump_backtrace.part.0+0xcc/0xe0
> [ 34.994932] show_stack+0x18/0x6c
> [ 34.995094] dump_stack_lvl+0x68/0x84
> [ 34.995276] dump_stack+0x18/0x34
> [ 34.995484] panic+0x16c/0x354
> [ 34.995673] __hyp_pgtable_total_pages+0x0/0x60
> [ 34.995933] scan_block+0x74/0x12c
> [ 34.996129] scan_gray_list+0xd8/0x19c
> [ 34.996332] kmemleak_scan+0x2c8/0x580
> [ 34.996535] kmemleak_write+0x340/0x4a0
> [ 34.996744] full_proxy_write+0x60/0xbc
> [ 34.996967] vfs_write+0xc4/0x2b0
> [ 34.997136] ksys_write+0x68/0xf4
> [ 34.997311] __arm64_sys_write+0x20/0x2c
> [ 34.997532] invoke_syscall+0x48/0x114
> [ 34.997779] el0_svc_common.constprop.0+0x44/0xec
> [ 34.998029] do_el0_svc+0x2c/0xc0
> [ 34.998205] el0_svc+0x2c/0x84
> [ 34.998421] el0t_64_sync_handler+0xf4/0x100
> [ 34.998653] el0t_64_sync+0x18c/0x190
> [ 34.999252] SMP: stopping secondary CPUs
> [ 35.000034] Kernel Offset: disabled
> [ 35.000261] CPU features: 0x800,00007831,00001086
> [ 35.000642] Memory Limit: none
> [ 35.001329] ---[ end Kernel panic - not syncing: HYP panic:
> [ 35.001329] PS:600003c9 PC:0000f418011a3750 ESR:00000000f2000800
> [ 35.001329] FAR:ffff000439200000 HPFAR:0000000004792000 PAR:0000000000000000
> [ 35.001329] VCPU:0000000000000000 ]---
>
> Fix this by explicitly excluding the hypervisor's memory pool from
> kmemleak like we already do for the hyp BSS.
>
> Cc: Mike Rapoport <rppt@xxxxxxxxxx>
> Fixes: a7259df76702 ("memblock: make memblock_find_in_range method private")
> Signed-off-by: Quentin Perret <qperret@xxxxxxxxxx>
> ---
> An alternative could be to actually exclude memory allocated using
> memblock_phys_alloc_range() from kmemleak scans to revert back to the
> old behaviour.
This would be wrong because memblock_phys_alloc() does allocate memory and
unless there is a good reason to exclude it from kmemleak.
> But nobody else has complained about this AFAIK, so I'd be inclined to
> keep this local to pKVM. No strong opinion.
Yes, please :)
An alternative to excluding this memory from kmemleak is to allocate it
using
memblock_phys_alloc_range(size, align, 0, MEMBLOCK_ALLOC_NOLEAKTRACE)
then it won't be added to kmemleak at the first place.
> ---
> arch/arm64/kvm/arm.c | 6 +++---
> 1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
> index 400bb0fe2745..28765bd22efb 100644
> --- a/arch/arm64/kvm/arm.c
> +++ b/arch/arm64/kvm/arm.c
> @@ -2110,11 +2110,11 @@ static int finalize_hyp_mode(void)
> return 0;
>
> /*
> - * Exclude HYP BSS from kmemleak so that it doesn't get peeked
> - * at, which would end badly once the section is inaccessible.
> - * None of other sections should ever be introspected.
> + * Exclude HYP sections from kmemleak so that they don't get peeked
> + * at, which would end badly once inaccessible.
> */
> kmemleak_free_part(__hyp_bss_start, __hyp_bss_end - __hyp_bss_start);
> + kmemleak_free_part(__va(hyp_mem_base), hyp_mem_size);
> return pkvm_drop_host_privileges();
> }
>
> --
> 2.36.1.476.g0c4daa206d-goog
>
--
Sincerely yours,
Mike.
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