Re: [PATCH v6 23/26] powerpc/pseries: Pass PLPKS password on kexec

[Stefan Berger <stefanb@linux.ibm.com>]

On 2/10/23 03:03, Andrew Donnellan wrote:
> From: Russell Currey <ruscur@russell.cc>
> 
> Before interacting with the PLPKS, we ask the hypervisor to generate a
> password for the current boot, which is then required for most further
> PLPKS operations.
> 
> If we kexec into a new kernel, the new kernel will try and fail to
> generate a new password, as the password has already been set.
> 
> Pass the password through to the new kernel via the device tree, in
> /chosen/ibm,plpks-pw. Check for the presence of this property before
> trying to generate a new password - if it exists, use the existing
> password and remove it from the device tree.
> 
> This only works with the kexec_file_load() syscall, not the older
> kexec_load() syscall, however if you're using Secure Boot then you want
> to be using kexec_file_load() anyway.
> 
> Signed-off-by: Russell Currey <ruscur@russell.cc>
> Signed-off-by: Andrew Donnellan <ajd@linux.ibm.com>
> 
> ---
> 
> v3: New patch
> 
> v4: Fix compile when CONFIG_PSERIES_PLPKS=n (snowpatch)
> 
>      Fix error handling on fdt_path_offset() call (ruscur)
> 
> v5: Fix DT property name in commit message (npiggin)
> 
>      Clear prop in FDT during init to prevent password exposure (mpe)
> 
>      Rework to remove ifdefs from C code (npiggin)
> 
> v6: Rebase on top of 7294194b47e994753a86eee8cf1c61f3f36458a3 and
>      fc546faa559538fb312c77e055243ece18ab3288
> 
>      Whitespace (stefanb)
> 
>      Use more const (stefanb)
> 
>      Get rid of FDT extra space allocation for node overhead, as it
>      shouldn't be necessary (ruscur)
> 
>      Note kexec_file_load() restriction in commit message
> ---
>   arch/powerpc/include/asm/plpks.h       | 14 ++++++
>   arch/powerpc/kernel/prom.c             |  4 ++
>   arch/powerpc/kexec/file_load_64.c      | 18 +++++---
>   arch/powerpc/platforms/pseries/plpks.c | 61 ++++++++++++++++++++++++++
>   4 files changed, 92 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/powerpc/include/asm/plpks.h b/arch/powerpc/include/asm/plpks.h
> index 757313e00521..23b77027c916 100644
> --- a/arch/powerpc/include/asm/plpks.h
> +++ b/arch/powerpc/include/asm/plpks.h
> @@ -176,6 +176,20 @@ u64 plpks_get_signedupdatealgorithms(void);
>    */
>   u16 plpks_get_passwordlen(void);
>   
> +/**
> + * Called in early init to retrieve and clear the PLPKS password from the DT.
> + */
> +void plpks_early_init_devtree(void);
> +
> +/**
> + * Populates the FDT with the PLPKS password to prepare for kexec.
> + */
> +int plpks_populate_fdt(void *fdt);
> +#else // CONFIG_PSERIES_PLPKS
> +static inline bool plpks_is_available(void) { return false; }
> +static inline u16 plpks_get_passwordlen(void) { BUILD_BUG(); }
> +static inline void plpks_early_init_devtree(void) { }
> +static inline int plpks_populate_fdt(void *fdt) { BUILD_BUG(); }
>   #endif // CONFIG_PSERIES_PLPKS
>   
>   #endif // _ASM_POWERPC_PLPKS_H
> diff --git a/arch/powerpc/kernel/prom.c b/arch/powerpc/kernel/prom.c
> index 4f1c920aa13e..8a13b378770f 100644
> --- a/arch/powerpc/kernel/prom.c
> +++ b/arch/powerpc/kernel/prom.c
> @@ -56,6 +56,7 @@
>   #include <asm/drmem.h>
>   #include <asm/ultravisor.h>
>   #include <asm/prom.h>
> +#include <asm/plpks.h>
>   
>   #include <mm/mmu_decl.h>
>   
> @@ -893,6 +894,9 @@ void __init early_init_devtree(void *params)
>   		powerpc_firmware_features |= FW_FEATURE_PS3_POSSIBLE;
>   #endif
>   
> +	/* If kexec left a PLPKS password in the DT, get it and clear it */
> +	plpks_early_init_devtree();
> +
>   	tm_init();
>   
>   	DBG(" <- early_init_devtree()\n");
> diff --git a/arch/powerpc/kexec/file_load_64.c b/arch/powerpc/kexec/file_load_64.c
> index 52085751f5f4..8a9469e1ce71 100644
> --- a/arch/powerpc/kexec/file_load_64.c
> +++ b/arch/powerpc/kexec/file_load_64.c
> @@ -27,6 +27,7 @@
>   #include <asm/kexec_ranges.h>
>   #include <asm/crashdump-ppc64.h>
>   #include <asm/prom.h>
> +#include <asm/plpks.h>
>   
>   struct umem_info {
>   	u64 *buf;		/* data buffer for usable-memory property */
> @@ -977,12 +978,17 @@ static unsigned int cpu_node_size(void)
>    */
>   unsigned int kexec_extra_fdt_size_ppc64(struct kimage *image)
>   {
> -	unsigned int cpu_nodes, extra_size;
> +	unsigned int cpu_nodes, extra_size = 0;
>   	struct device_node *dn;
>   	u64 usm_entries;
>   
> +	// Budget some space for the password blob. There's already extra space
> +	// for the key name
> +	if (plpks_is_available())
> +		extra_size += (unsigned int)plpks_get_passwordlen();
> +
>   	if (image->type != KEXEC_TYPE_CRASH)
> -		return 0;
> +		return extra_size;
>   
>   	/*
>   	 * For kdump kernel, account for linux,usable-memory and
> @@ -992,9 +998,7 @@ unsigned int kexec_extra_fdt_size_ppc64(struct kimage *image)
>   	if (drmem_lmb_size()) {
>   		usm_entries = ((memory_hotplug_max() / drmem_lmb_size()) +
>   			       (2 * (resource_size(&crashk_res) / drmem_lmb_size())));
> -		extra_size = (unsigned int)(usm_entries * sizeof(u64));
> -	} else {
> -		extra_size = 0;
> +		extra_size += (unsigned int)(usm_entries * sizeof(u64));
>   	}
>   
>   	/*
> @@ -1233,6 +1237,10 @@ int setup_new_fdt_ppc64(const struct kimage *image, void *fdt,
>   		}
>   	}
>   
> +	// If we have PLPKS active, we need to provide the password to the new kernel
> +	if (plpks_is_available())
> +		ret = plpks_populate_fdt(fdt);
> +
>   out:
>   	kfree(rmem);
>   	kfree(umem);
> diff --git a/arch/powerpc/platforms/pseries/plpks.c b/arch/powerpc/platforms/pseries/plpks.c
> index 671a10acaebf..cdf09e5bd741 100644
> --- a/arch/powerpc/platforms/pseries/plpks.c
> +++ b/arch/powerpc/platforms/pseries/plpks.c
> @@ -16,6 +16,9 @@
>   #include <linux/slab.h>
>   #include <linux/string.h>
>   #include <linux/types.h>
> +#include <linux/of_fdt.h>
> +#include <linux/libfdt.h>
> +#include <linux/memblock.h>
>   #include <asm/hvcall.h>
>   #include <asm/machdep.h>
>   #include <asm/plpks.h>
> @@ -128,6 +131,12 @@ static int plpks_gen_password(void)
>   	u8 *password, consumer = PLPKS_OS_OWNER;
>   	int rc;
>   
> +	// If we booted from kexec, we could be reusing an existing password already
> +	if (ospassword) {
> +		pr_debug("Password of length %u already in use\n", ospasswordlength);
> +		return 0;
> +	}
> +
>   	// The password must not cross a page boundary, so we align to the next power of 2
>   	password = kzalloc(roundup_pow_of_two(maxpwsize), GFP_KERNEL);
>   	if (!password)
> @@ -621,6 +630,58 @@ int plpks_read_bootloader_var(struct plpks_var *var)
>   	return plpks_read_var(PLPKS_BOOTLOADER_OWNER, var);
>   }
>   
> +int plpks_populate_fdt(void *fdt)
> +{
> +	int chosen_offset = fdt_path_offset(fdt, "/chosen");
> +
> +	if (chosen_offset < 0) {
> +		pr_err("Can't find chosen node: %s\n",
> +		       fdt_strerror(chosen_offset));
> +		return chosen_offset;
> +	}
> +
> +	return fdt_setprop(fdt, chosen_offset, "ibm,plpks-pw", ospassword, ospasswordlength);
> +}
> +
> +// Once a password is registered with the hypervisor it cannot be cleared without
> +// rebooting the LPAR, so to keep using the PLPKS across kexec boots we need to
> +// recover the previous password from the FDT.
> +//
> +// There are a few challenges here.  We don't want the password to be visible to
> +// users, so we need to clear it from the FDT.  This has to be done in early boot.
> +// Clearing it from the FDT would make the FDT's checksum invalid, so we have to
> +// manually cause the checksum to be recalculated.
> +void __init plpks_early_init_devtree(void)
> +{
> +	void *fdt = initial_boot_params;
> +	int chosen_node = fdt_path_offset(fdt, "/chosen");
> +	const u8 *password;
> +	int len;
> +
> +	if (chosen_node < 0)
> +		return;
> +
> +	password = fdt_getprop(fdt, chosen_node, "ibm,plpks-pw", &len);
> +	if (len <= 0) {
> +		pr_debug("Couldn't find ibm,plpks-pw node.\n");
> +		return;
> +	}
> +
> +	ospassword = memblock_alloc_raw(len, SMP_CACHE_BYTES);
> +	if (!ospassword) {
> +		pr_err("Error allocating memory for password.\n");
> +		goto out;
> +	}
> +
> +	memcpy(ospassword, password, len);
> +	ospasswordlength = (u16)len;
> +
> +out:
> +	fdt_nop_property(fdt, chosen_node, "ibm,plpks-pw");
> +	// Since we've cleared the password, we must update the FDT checksum
> +	early_init_dt_verify(fdt);
> +}
> +
>   static __init int pseries_plpks_init(void)
>   {
>   	int rc;

Reviewed-by: Stefan Berger <stefanb@linux.ibm.com>