Re: [PATCH v3 4/4] RISC-V: Use Zkr to seed KASLR base address

Charlie Jenkins
2024-07-02T04:31:02Z

On Mon, Jul 01, 2024 at 02:51:32PM -0400, Jesse Taube wrote:
> Parse the device tree for Zkr in the isa string.
> If Zkr is present, use it to seed the kernel base address.
>
> On an ACPI system, as of this commit, there is no easy way to check if
> Zkr is present. Blindly running the instruction isn't an option as;
> we have to be able to trust the firmware.
>
> Signed-off-by: Jesse Taube <jesse@rivosinc.com>
> ---
> V1 -> V2:
> - Almost entire rewrite
> V2 -> V3:
> - Dont parse iscv,isa-base
> - Move fdt_early_match_extension_isa in pi.h under comment
> - Only check enabled cpus
> - Rename early_isa_str to fdt_early_match_extension_isa
> - Rename get_ext_named to early_cpu_isa_ext_available
> - Rewrite isa_string_contains
> - Update commit description
> - Use fdt_stringlist_contains for riscv,isa-extensions
> ---
> arch/riscv/kernel/pi/Makefile | 2 +-
> arch/riscv/kernel/pi/archrandom_early.c | 30 +++++
> arch/riscv/kernel/pi/fdt_early.c | 160 ++++++++++++++++++++++++
> arch/riscv/kernel/pi/pi.h | 3 +
> arch/riscv/mm/init.c | 5 +-
> 5 files changed, 198 insertions(+), 2 deletions(-)
> create mode 100644 arch/riscv/kernel/pi/archrandom_early.c
>
> diff --git a/arch/riscv/kernel/pi/Makefile b/arch/riscv/kernel/pi/Makefile
> index 1ef7584be0c3..dba902f2a538 100644
> --- a/arch/riscv/kernel/pi/Makefile
> +++ b/arch/riscv/kernel/pi/Makefile
> @@ -33,5 +33,5 @@ $(obj)/string.o: $(srctree)/lib/string.c FORCE
> $(obj)/ctype.o: $(srctree)/lib/ctype.c FORCE
> $(call if_changed_rule,cc_o_c)
>
> -obj-y := cmdline_early.pi.o fdt_early.pi.o string.pi.o ctype.pi.o lib-fdt.pi.o lib-fdt_ro.pi.o
> +obj-y := cmdline_early.pi.o fdt_early.pi.o string.pi.o ctype.pi.o lib-fdt.pi.o lib-fdt_ro.pi.o archrandom_early.pi.o

When CONFIG_FORTIFY_SOURCE is enabled, the string functions try to
reference `__fortify_panic` which gets aliased to `__pi___fortify_panic`
and causes lld to fail:

ld.lld: error: undefined hidden symbol: __pi___fortify_panic
>>> referenced by fdt_early.c:24 (arch/riscv/kernel/pi/fdt_early.c:24)
>>> arch/riscv/kernel/pi/fdt_early.pi.o:(__pi_fdt_early_match_extension_isa) in archive vmlinux.a

This early in boot __fortify_panic isn't supported. Can you add
`CFLAGS_fdt_early.o += -D__NO_FORTIFY` next to the same addition for
cmdline_early and fdt_early?

The rest of this looks go to me (just send a new version with this simple fix).

Reviewed-by: Charlie Jenkins <charlie@rivosinc.com>

> extra-y := $(patsubst %.pi.o,%.o,$(obj-y))
> diff --git a/arch/riscv/kernel/pi/archrandom_early.c b/arch/riscv/kernel/pi/archrandom_early.c
> new file mode 100644
> index 000000000000..3f05d3cf3b7b
> --- /dev/null
> +++ b/arch/riscv/kernel/pi/archrandom_early.c
> @@ -0,0 +1,30 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +
> +#include <asm/csr.h>
> +#include <linux/processor.h>
> +
> +#include "pi.h"
> +
> +/*
> + * To avoid rewriting code include asm/archrandom.h and create macros
> + * for the functions that won't be included.
> + */
> +#undef riscv_has_extension_unlikely
> +#define riscv_has_extension_likely(...) false
> +#undef pr_err_once
> +#define pr_err_once(...)
> +
> +#include <asm/archrandom.h>
> +
> +u64 get_kaslr_seed_zkr(const uintptr_t dtb_pa)
> +{
> + unsigned long seed = 0;
> +
> + if (!fdt_early_match_extension_isa((const void *)dtb_pa, "zkr"))
> + return 0;
> +
> + if (!csr_seed_long(&seed))
> + return 0;
> +
> + return seed;
> +}
> diff --git a/arch/riscv/kernel/pi/fdt_early.c b/arch/riscv/kernel/pi/fdt_early.c
> index 40ee299702bf..49ff5360bf87 100644
> --- a/arch/riscv/kernel/pi/fdt_early.c
> +++ b/arch/riscv/kernel/pi/fdt_early.c
> @@ -2,6 +2,7 @@
> #include <linux/types.h>
> #include <linux/init.h>
> #include <linux/libfdt.h>
> +#include <linux/ctype.h>
>
> #include "pi.h"
>
> @@ -23,3 +24,162 @@ u64 get_kaslr_seed(uintptr_t dtb_pa)
> *prop = 0;
> return ret;
> }
> +
> +/**
> + * fdt_device_is_available - check if a device is available for use
> + *
> + * @fdt: pointer to the device tree blob
> + * @node: offset of the node whose property to find
> + *
> + * Returns true if the status property is absent or set to "okay" or "ok",
> + * false otherwise
> + */
> +static bool fdt_device_is_available(const void *fdt, int node)
> +{
> + const char *status;
> + int statlen;
> +
> + status = fdt_getprop(fdt, node, "status", &statlen);
> + if (!status)
> + return true;
> +
> + if (statlen > 0) {
> + if (!strcmp(status, "okay") || !strcmp(status, "ok"))
> + return true;
> + }
> +
> + return false;
> +}
> +
> +/* Copy of fdt_nodename_eq_ */
> +static int fdt_node_name_eq(const void *fdt, int offset,
> + const char *s)
> +{
> + int olen;
> + int len = strlen(s);
> + const char *p = fdt_get_name(fdt, offset, &olen);
> +
> + if (!p || olen < len)
> + /* short match */
> + return 0;
> +
> + if (memcmp(p, s, len) != 0)
> + return 0;
> +
> + if (p[len] == '\0')
> + return 1;
> + else if (!memchr(s, '@', len) && (p[len] == '@'))
> + return 1;
> + else
> + return 0;
> +}
> +
> +/**
> + * isa_string_contains - check if isa string contains an extension
> + *
> + * @isa_str: isa string to search
> + * @ext_name: the extension to search for
> + *
> + * Returns true if the extension is in the given isa string,
> + * false otherwise
> + */
> +static bool isa_string_contains(const char *isa_str, const char *ext_name)
> +{
> + size_t i, single_end, len = strlen(ext_name);
> + char ext_end;
> +
> + /* Error must contain rv32/64 */
> + if (strlen(isa_str) < 4)
> + return false;
> +
> + if (len == 1) {
> + single_end = strcspn(isa_str, "sSxXzZ");
> + /* Search for single chars between rv32/64 and multi-letter extensions */
> + for (i = 4; i < single_end; i++) {
> + if (tolower(isa_str[i]) == ext_name[0])
> + return true;
> + }
> + return false;
> + }
> +
> + /* Skip to start of multi-letter extensions */
> + isa_str = strpbrk(isa_str, "sSxXzZ");
> + while (isa_str) {
> + if (strncasecmp(isa_str, ext_name, len) == 0) {
> + ext_end = isa_str[len];
> + /* Check if matches the whole extension excluding version. */
> + if (ext_end == '\0' || ext_end == '_' || isdigit(ext_end))
> + return true;
> + }
> + /* Multi-letter extensions must be split from other multi-letter
> + * extensions with an "_", the end of a multi-letter extension will
> + * either be the null character or the "_" at the start of the next
> + * multi-letter extension.
> + */
> + isa_str = strchr(isa_str, '_');
> + if (isa_str)
> + isa_str++;
> + }
> +
> + return false;
> +}
> +
> +/**
> + * early_cpu_isa_ext_available - check if cpu node has an extension
> + *
> + * @fdt: pointer to the device tree blob
> + * @node: offset of the cpu node
> + * @ext_name: the extension to search for
> + *
> + * Returns true if the cpu node has the extension,
> + * false otherwise
> + */
> +static bool early_cpu_isa_ext_available(const void *fdt, int node, const char *ext_name)
> +{
> + const void *prop;
> + int len;
> +
> + prop = fdt_getprop(fdt, node, "riscv,isa-extensions", &len);
> + if (prop && fdt_stringlist_contains(prop, len, ext_name))
> + return true;
> +
> + prop = fdt_getprop(fdt, node, "riscv,isa", &len);
> + if (prop && isa_string_contains(prop, ext_name))
> + return true;
> +
> + return false;
> +}
> +
> +/**
> + * fdt_early_match_extension_isa - check if all cpu nodes have an extension
> + *
> + * @fdt: pointer to the device tree blob
> + * @ext_name: the extension to search for
> + *
> + * Returns true if the all available the cpu nodes have the extension,
> + * false otherwise
> + */
> +bool fdt_early_match_extension_isa(const void *fdt, const char *ext_name)
> +{
> + int node, parent;
> + bool ret = false;
> +
> + parent = fdt_path_offset(fdt, "/cpus");
> + if (parent < 0)
> + return false;
> +
> + fdt_for_each_subnode(node, fdt, parent) {
> + if (!fdt_node_name_eq(fdt, node, "cpu"))
> + continue;
> +
> + if (!fdt_device_is_available(fdt, node))
> + continue;
> +
> + if (!early_cpu_isa_ext_available(fdt, node, ext_name))
> + return false;
> +
> + ret = true;
> + }
> +
> + return ret;
> +}
> diff --git a/arch/riscv/kernel/pi/pi.h b/arch/riscv/kernel/pi/pi.h
> index 493c8cb7c0e6..21141d84fea6 100644
> --- a/arch/riscv/kernel/pi/pi.h
> +++ b/arch/riscv/kernel/pi/pi.h
> @@ -11,7 +11,10 @@
> */
>
> u64 get_kaslr_seed(uintptr_t dtb_pa);
> +u64 get_kaslr_seed_zkr(const uintptr_t dtb_pa);
> bool set_nokaslr_from_cmdline(uintptr_t dtb_pa);
> u64 set_satp_mode_from_cmdline(uintptr_t dtb_pa);
>
> +bool fdt_early_match_extension_isa(const void *fdt, const char *ext_name);
> +
> #endif /* _RISCV_PI_H_ */
> diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
> index 9940171c79f0..bfb068dc4a64 100644
> --- a/arch/riscv/mm/init.c
> +++ b/arch/riscv/mm/init.c
> @@ -1025,6 +1025,7 @@ static void __init pt_ops_set_late(void)
> #ifdef CONFIG_RANDOMIZE_BASE
> extern bool __init __pi_set_nokaslr_from_cmdline(uintptr_t dtb_pa);
> extern u64 __init __pi_get_kaslr_seed(uintptr_t dtb_pa);
> +extern u64 __init __pi_get_kaslr_seed_zkr(const uintptr_t dtb_pa);
>
> static int __init print_nokaslr(char *p)
> {
> @@ -1045,10 +1046,12 @@ asmlinkage void __init setup_vm(uintptr_t dtb_pa)
>
> #ifdef CONFIG_RANDOMIZE_BASE
> if (!__pi_set_nokaslr_from_cmdline(dtb_pa)) {
> - u64 kaslr_seed = __pi_get_kaslr_seed(dtb_pa);
> + u64 kaslr_seed = __pi_get_kaslr_seed_zkr(dtb_pa);
> u32 kernel_size = (uintptr_t)(&_end) - (uintptr_t)(&_start);
> u32 nr_pos;
>
> + if (kaslr_seed == 0)
> + kaslr_seed = __pi_get_kaslr_seed(dtb_pa);
> /*
> * Compute the number of positions available: we are limited
> * by the early page table that only has one PUD and we must
> --
> 2.45.2
>
>
> _______________________________________________
> linux-riscv mailing list
> linux-riscv@lists.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-riscv