[PATCH v3 22/60] arm64: idreg-override: Avoid kstrtou64() to parse a single hex digit

Ard Biesheuvel
2023-03-07T14:09:14Z

All ID register value overrides are =0 with the exception of the nokaslr
pseudo feature which uses =1. In order to remove the dependency on
kstrtou64(), which is part of the core kernel and no longer usable once
we move idreg-override into the early mini C runtime, let's just parse a
single hex digit (with optional leading 0x) and set the output value
accordingly.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
---
arch/arm64/kernel/idreg-override.c | 16 +++++++++++++++-
1 file changed, 15 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/kernel/idreg-override.c b/arch/arm64/kernel/idreg-override.c
index 58c02fe20e1050b4..758f0e86e2bd2a34 100644
--- a/arch/arm64/kernel/idreg-override.c
+++ b/arch/arm64/kernel/idreg-override.c
@@ -195,6 +195,20 @@ static const struct {
{ "nokaslr", "arm64_sw.nokaslr=1" },
};

+static int __init parse_hexdigit(const char *p, u64 *v)
+{
+ // skip "0x" if it comes next
+ if (p[0] == '0' && tolower(p[1]) == 'x')
+ p += 2;
+
+ // check whether the RHS is a single hex digit
+ if (!isxdigit(p[0]) || (p[1] && !isspace(p[1])))
+ return -EINVAL;
+
+ *v = tolower(*p) - (isdigit(*p) ? '0' : 'a' - 10);
+ return 0;
+}
+
static int __init find_field(const char *cmdline, char *opt, int len,
const struct ftr_set_desc *reg, int f, u64 *v)
{
@@ -208,7 +222,7 @@ static int __init find_field(const char *cmdline, char *opt, int len,
if (memcmp(cmdline, opt, len))
return -1;

- return kstrtou64(cmdline + len, 0, v);
+ return parse_hexdigit(cmdline + len, v);
}

static void __init match_options(const char *cmdline)
--
2.39.2