Re: [PATCH] iscsi_ibft: fix crash due to KASLR physical memory remapping

Mike Rapoport
2021-07-26T18:09:29Z

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On Mon, Jul 26, 2021 at 01:04:25PM +0200, Maurizio Lombardi wrote:
> Starting with commit a799c2bd29d1
> ("x86/setup: Consolidate early memory reservations"),
> memory reservations have been moved earlier during the boot process,
> before the execution of the Kernel Address Space Layout Randomization code.
>
> setup_arch() calls the iscsi_ibft's find_ibft_region() function
> to find and reserve the memory dedicated to the iBFT; this function
> also saves a (virt) pointer to the iBFT table for later use.

^ virtual
>
> The problem is that if KALSR is active, the physical memory gets
> remapped somewhere else in the virtual address space and the pointer is
> no longer valid, this will cause a kernel panic when the iscsi driver tries
> to dereference it.
>
> This patch fixes the bug by saving the address of the physical location

Please drop "this patch" and use imperative language, e.g. "Fix this bug
by..."

> of the ibft; later the driver will use isa_bus_to_virt() to get
> the correct virtual address.
>
> It will also simplify the code by renaming find_ibft_region()
> to reserve_ibft_region() and removing all the wrappers.
>
> [ 37.764225] iBFT detected.

It is better to put the crash report close to the problem description as it
actually shows how the issue is manifested.

> [ 37.778877] BUG: unable to handle page fault for address: ffff888000099fd8
> [ 37.816542] #PF: supervisor read access in kernel mode
> [ 37.844304] #PF: error_code(0x0000) - not-present page
> [ 37.872857] PGD 0 P4D 0
> [ 37.886985] Oops: 0000 [#1] SMP PTI
> [ 37.904809] CPU: 46 PID: 1073 Comm: modprobe Tainted: G X --------- --- 5.13.0-0.rc2.19.el9.x86_64 #1
> [ 37.956525] Hardware name: HP ProLiant DL580 G7, BIOS P65 10/01/2013
> [ 37.987170] RIP: 0010:ibft_init+0x3e/0xd42 [iscsi_ibft]
> [ 38.012976] Code: 04 25 28 00 00 00 48 89 44 24 08 31 c0 48 83 3d e1 cc 7e d7 00 74 28 48 c7 c7 21 81 1b c0 e8 b3 10 81 d5 48 8b 05 cc cc 7e d7 <0f> b6 70 08 48 63 50 04 40 80 fe 01 75 5e 31 f6 48 01 c2 eb 6e 83
> [ 38.106835] RSP: 0018:ffffb7d288fc3db0 EFLAGS: 00010246
> [ 38.131341] RAX: ffff888000099fd0 RBX: 0000000000000000 RCX: 0000000000000000
> [ 38.167110] RDX: 0000000000000000 RSI: ffff9ba7efb97c80 RDI: ffff9ba7efb97c80
> [ 38.200777] RBP: ffffffffc01c82be R08: 0000000000000000 R09: ffffb7d288fc3bf0
> [ 38.237188] R10: ffffb7d288fc3be8 R11: ffffffff96de70a8 R12: ffff9ba4059d6400
> [ 38.270940] R13: 000055689f1ac050 R14: 000055689df18962 R15: ffffb7d288fc3e78
> [ 38.307167] FS: 00007f9546720b80(0000) GS:ffff9ba7efb80000(0000) knlGS:0000000000000000
> [ 38.351204] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [ 38.381034] CR2: ffff888000099fd8 CR3: 000000044175e004 CR4: 00000000000206e0
> [ 38.419938] Call Trace:
> [ 38.432679] ? ibft_create_kobject+0x1d2/0x1d2 [iscsi_ibft]
> [ 38.462584] do_one_initcall+0x44/0x1d0
> [ 38.480856] ? kmem_cache_alloc_trace+0x119/0x220
> [ 38.505554] do_init_module+0x5c/0x270
> [ 38.526578] __do_sys_init_module+0x12e/0x1b0
> [ 38.548699] do_syscall_64+0x40/0x80
> [ 38.565679] entry_SYSCALL_64_after_hwframe+0x44/0xae
>
> Signed-off-by: Maurizio Lombardi <mlombard@redhat.com>
> ---
> arch/x86/kernel/setup.c | 10 -------
> drivers/firmware/iscsi_ibft.c | 10 +++++--
> drivers/firmware/iscsi_ibft_find.c | 48 +++++++++++-------------------
> include/linux/iscsi_ibft.h | 14 ++++-----
> 4 files changed, 30 insertions(+), 52 deletions(-)
>
> diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
> index bff3a784aec5..63b20536c8d2 100644
> --- a/arch/x86/kernel/setup.c
> +++ b/arch/x86/kernel/setup.c
> @@ -572,16 +572,6 @@ void __init reserve_standard_io_resources(void)
>
> }
>
> -static __init void reserve_ibft_region(void)
> -{
> - unsigned long addr, size = 0;
> -
> - addr = find_ibft_region(&size);
> -
> - if (size)
> - memblock_reserve(addr, size);
> -}
> -
> static bool __init snb_gfx_workaround_needed(void)
> {
> #ifdef CONFIG_PCI
> diff --git a/drivers/firmware/iscsi_ibft.c b/drivers/firmware/iscsi_ibft.c
> index 7127a04bca19..612a59e213df 100644
> --- a/drivers/firmware/iscsi_ibft.c
> +++ b/drivers/firmware/iscsi_ibft.c
> @@ -84,8 +84,10 @@ MODULE_DESCRIPTION("sysfs interface to BIOS iBFT information");
> MODULE_LICENSE("GPL");
> MODULE_VERSION(IBFT_ISCSI_VERSION);
>
> +static struct acpi_table_ibft *ibft_addr;
> +
> #ifndef CONFIG_ISCSI_IBFT_FIND
> -struct acpi_table_ibft *ibft_addr;
> +phys_addr_t ibft_phys_addr;
> #endif
>
> struct ibft_hdr {
> @@ -858,11 +860,13 @@ static int __init ibft_init(void)
> int rc = 0;
>
> /*
> - As on UEFI systems the setup_arch()/find_ibft_region()
> + As on UEFI systems the setup_arch()/reserve_ibft_region()
> is called before ACPI tables are parsed and it only does
> legacy finding.
> */
> - if (!ibft_addr)
> + if (ibft_phys_addr)
> + ibft_addr = isa_bus_to_virt(ibft_phys_addr);
> + else
> acpi_find_ibft_region();
>
> if (ibft_addr) {
> diff --git a/drivers/firmware/iscsi_ibft_find.c b/drivers/firmware/iscsi_ibft_find.c
> index 64bb94523281..a0594590847d 100644
> --- a/drivers/firmware/iscsi_ibft_find.c
> +++ b/drivers/firmware/iscsi_ibft_find.c
> @@ -31,8 +31,8 @@
> /*
> * Physical location of iSCSI Boot Format Table.
> */
> -struct acpi_table_ibft *ibft_addr;
> -EXPORT_SYMBOL_GPL(ibft_addr);
> +phys_addr_t ibft_phys_addr;
> +EXPORT_SYMBOL_GPL(ibft_phys_addr);
>
> static const struct {
> char *sign;
> @@ -47,13 +47,24 @@ static const struct {
> #define VGA_MEM 0xA0000 /* VGA buffer */
> #define VGA_SIZE 0x20000 /* 128kB */
>
> -static int __init find_ibft_in_mem(void)
> +/*
> + * Routine used to find and reserve the iSCSI Boot Format Table
> + */
> +void __init reserve_ibft_region(void)
> {
> unsigned long pos;
> unsigned int len = 0;
> void *virt;
> int i;
>
> + ibft_phys_addr = 0;
> +
> + /* iBFT 1.03 section 1.4.3.1 mandates that UEFI machines will
> + * only use ACPI for this
> + */
> + if (efi_enabled(EFI_BOOT))
> + return;
> +
> for (pos = IBFT_START; pos < IBFT_END; pos += 16) {
> /* The table can't be inside the VGA BIOS reserved space,
> * so skip that area */
> @@ -70,35 +81,12 @@ static int __init find_ibft_in_mem(void)
> /* if the length of the table extends past 1M,
> * the table cannot be valid. */
> if (pos + len <= (IBFT_END-1)) {
> - ibft_addr = (struct acpi_table_ibft *)virt;
> - pr_info("iBFT found at 0x%lx.\n", pos);
> - goto done;
> + ibft_phys_addr = pos;
> + memblock_reserve(ibft_phys_addr, PAGE_ALIGN(len));
> + pr_info("iBFT found at 0x%lx.\n", ibft_phys_addr);
> + return;
> }
> }
> }
> }
> -done:
> - return len;
> -}
> -/*
> - * Routine used to find the iSCSI Boot Format Table. The logical
> - * kernel address is set in the ibft_addr global variable.
> - */
> -unsigned long __init find_ibft_region(unsigned long *sizep)
> -{
> - ibft_addr = NULL;
> -
> - /* iBFT 1.03 section 1.4.3.1 mandates that UEFI machines will
> - * only use ACPI for this */
> -
> - if (!efi_enabled(EFI_BOOT))
> - find_ibft_in_mem();
> -
> - if (ibft_addr) {
> - *sizep = PAGE_ALIGN(ibft_addr->header.length);
> - return (u64)virt_to_phys(ibft_addr);
> - }
> -
> - *sizep = 0;
> - return 0;
> }
> diff --git a/include/linux/iscsi_ibft.h b/include/linux/iscsi_ibft.h
> index b7b45ca82bea..a80539c6eeec 100644
> --- a/include/linux/iscsi_ibft.h
> +++ b/include/linux/iscsi_ibft.h
> @@ -13,26 +13,22 @@
> #ifndef ISCSI_IBFT_H
> #define ISCSI_IBFT_H
>
> -#include <linux/acpi.h>
> +#include <linux/types.h>
>
> /*
> * Logical location of iSCSI Boot Format Table.
> * If the value is NULL there is no iBFT on the machine.
> */
> -extern struct acpi_table_ibft *ibft_addr;
> +extern phys_addr_t ibft_phys_addr;
>
> /*
> * Routine used to find and reserve the iSCSI Boot Format Table. The
> - * mapped address is set in the ibft_addr variable.
> + * physical address is set in the ibft_phys_addr variable.
> */
> #ifdef CONFIG_ISCSI_IBFT_FIND
> -unsigned long find_ibft_region(unsigned long *sizep);
> +void reserve_ibft_region(void);
> #else
> -static inline unsigned long find_ibft_region(unsigned long *sizep)
> -{
> - *sizep = 0;
> - return 0;
> -}
> +static inline void reserve_ibft_region(void) {}
> #endif
>
> #endif /* ISCSI_IBFT_H */
> --
> 2.27.0
>

--
Sincerely yours,
Mike.