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

Alexandre Ghiti
2024-07-02T06:46:09Z

Hi Jesse,

On Tue, Jul 2, 2024 at 6:30 AM Charlie Jenkins <charlie@rivosinc.com> wrote:
>
> 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?

With this ^ fixed, you can add:

Reviewed-by: Alexandre Ghiti <alexghiti@rivosinc.com>

Thanks,

Alex

>
> 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