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Subject[PATCH 01/12] efi/arm*: Only register page tables when they exist
Date
From: Mark Rutland <mark.rutland@arm.com>

Currently the arm/arm64 runtime code registers the runtime servies
pagetables with ptdump regardless of whether runtime services page
tables have been created.

As efi_mm.pgd is NULL in these cases, attempting to dump the efi page
tables results in a NULL pointer dereference in the ptdump code:

/sys/kernel/debug# cat efi_page_tables
[ 479.522600] Unable to handle kernel NULL pointer dereference at virtual address 00000000
[ 479.522715] Mem abort info:
[ 479.522764] ESR = 0x96000006
[ 479.522850] Exception class = DABT (current EL), IL = 32 bits
[ 479.522899] SET = 0, FnV = 0
[ 479.522937] EA = 0, S1PTW = 0
[ 479.528200] Data abort info:
[ 479.528230] ISV = 0, ISS = 0x00000006
[ 479.528317] CM = 0, WnR = 0
[ 479.528317] user pgtable: 4k pages, 48-bit VAs, pgd = 0000000064ab0cb0
[ 479.528449] [0000000000000000] *pgd=00000000fbbe4003, *pud=00000000fb66e003, *pmd=0000000000000000
[ 479.528600] Internal error: Oops: 96000006 [#1] PREEMPT SMP
[ 479.528664] Modules linked in:
[ 479.528699] CPU: 0 PID: 2457 Comm: cat Not tainted 4.15.0-rc3-00065-g2ad2ee7ecb5c-dirty #7
[ 479.528799] Hardware name: FVP Base (DT)
[ 479.528899] pstate: 00400009 (nzcv daif +PAN -UAO)
[ 479.528941] pc : walk_pgd.isra.1+0x20/0x1d0
[ 479.529011] lr : ptdump_walk_pgd+0x30/0x50
[ 479.529105] sp : ffff00000bf4bc20
[ 479.529185] x29: ffff00000bf4bc20 x28: 0000ffff9d22e000
[ 479.529271] x27: 0000000000020000 x26: ffff80007b4c63c0
[ 479.529358] x25: 00000000014000c0 x24: ffff80007c098900
[ 479.529445] x23: ffff00000bf4beb8 x22: 0000000000000000
[ 479.529532] x21: ffff00000bf4bd70 x20: 0000000000000001
[ 479.529618] x19: ffff00000bf4bcb0 x18: 0000000000000000
[ 479.529760] x17: 000000000041a1c8 x16: ffff0000082139d8
[ 479.529800] x15: 0000ffff9d3c6030 x14: 0000ffff9d2527f4
[ 479.529924] x13: 00000000000003f3 x12: 0000000000000038
[ 479.530000] x11: 0000000000000003 x10: 0101010101010101
[ 479.530099] x9 : 0000000017e94050 x8 : 000000000000003f
[ 479.530226] x7 : 0000000000000000 x6 : 0000000000000000
[ 479.530313] x5 : 0000000000000001 x4 : 0000000000000000
[ 479.530416] x3 : ffff000009069fd8 x2 : 0000000000000000
[ 479.530500] x1 : 0000000000000000 x0 : 0000000000000000
[ 479.530599] Process cat (pid: 2457, stack limit = 0x000000005d1b0e6f)
[ 479.530660] Call trace:
[ 479.530746] walk_pgd.isra.1+0x20/0x1d0
[ 479.530833] ptdump_walk_pgd+0x30/0x50
[ 479.530907] ptdump_show+0x10/0x20
[ 479.530920] seq_read+0xc8/0x470
[ 479.531023] full_proxy_read+0x60/0x90
[ 479.531100] __vfs_read+0x18/0x100
[ 479.531180] vfs_read+0x88/0x160
[ 479.531267] SyS_read+0x48/0xb0
[ 479.531299] el0_svc_naked+0x20/0x24
[ 479.531400] Code: 91400420 f90033a0 a90707a2 f9403fa0 (f9400000)
[ 479.531499] ---[ end trace bfe8e28d8acb2b67 ]---
Segmentation fault

Let's avoid this problem by only registering the tables after their
successful creation, which is also less confusing when EFI runtime
services are not in use.

Reported-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Acked-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
---
drivers/firmware/efi/arm-runtime.c | 3 +++
1 file changed, 3 insertions(+)

diff --git a/drivers/firmware/efi/arm-runtime.c b/drivers/firmware/efi/arm-runtime.c
index 1cc41c3d6315..86a1ad17a32e 100644
--- a/drivers/firmware/efi/arm-runtime.c
+++ b/drivers/firmware/efi/arm-runtime.c
@@ -54,6 +54,9 @@ static struct ptdump_info efi_ptdump_info = {

static int __init ptdump_init(void)
{
+ if (!efi_enabled(EFI_RUNTIME_SERVICES))
+ return 0;
+
return ptdump_debugfs_register(&efi_ptdump_info, "efi_page_tables");
}
device_initcall(ptdump_init);
--
2.15.1
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