[RFC 1/8] mpi: Introduce mpi_key_length()

From: Petr Tesarik <petrtesarik@huaweicloud.com>
To: Dave Hansen <dave.hansen@intel.com>
Cc: "Petr Tesařík" <petr@tesarici.cz>,
	"Petr Tesarik" <petrtesarik@huaweicloud.com>,
	"Jonathan Corbet" <corbet@lwn.net>,
	"Thomas Gleixner" <tglx@linutronix.de>,
	"Ingo Molnar" <mingo@redhat.com>,
	"Borislav Petkov" <bp@alien8.de>,
	"Dave Hansen" <dave.hansen@linux.intel.com>,
	"maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)"
	<x86@kernel.org>, "H. Peter Anvin" <hpa@zytor.com>,
	"Andy Lutomirski" <luto@kernel.org>,
	"Oleg Nesterov" <oleg@redhat.com>,
	"Peter Zijlstra" <peterz@infradead.org>,
	"Xin Li" <xin3.li@intel.com>, "Arnd Bergmann" <arnd@arndb.de>,
	"Andrew Morton" <akpm@linux-foundation.org>,
	"Rick Edgecombe" <rick.p.edgecombe@intel.com>,
	"Kees Cook" <keescook@chromium.org>,
	"Masami Hiramatsu (Google)" <mhiramat@kernel.org>,
	"Pengfei Xu" <pengfei.xu@intel.com>,
	"Josh Poimboeuf" <jpoimboe@kernel.org>,
	"Ze Gao" <zegao2021@gmail.com>,
	"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
	"Kai Huang" <kai.huang@intel.com>,
	"David Woodhouse" <dwmw@amazon.co.uk>,
	"Brian Gerst" <brgerst@gmail.com>,
	"Jason Gunthorpe" <jgg@ziepe.ca>,
	"Joerg Roedel" <jroedel@suse.de>,
	"Mike Rapoport (IBM)" <rppt@kernel.org>,
	"Tina Zhang" <tina.zhang@intel.com>,
	"Jacob Pan" <jacob.jun.pan@linux.intel.com>,
	"open list:DOCUMENTATION" <linux-doc@vger.kernel.org>,
	"open list" <linux-kernel@vger.kernel.org>,
	"Roberto Sassu" <roberto.sassu@huaweicloud.com>,
	"David Howells" <dhowells@redhat.com>,
	"Petr Tesarik" <petr.tesarik1@huawei-partners.com>
Subject: [RFC 1/8] mpi: Introduce mpi_key_length()
Date: Fri, 16 Feb 2024 16:24:28 +0100	[thread overview]
Message-ID: <20240216152435.1575-2-petrtesarik@huaweicloud.com> (raw)
In-Reply-To: <20240216152435.1575-1-petrtesarik@huaweicloud.com>

From: Roberto Sassu <roberto.sassu@huawei.com>

Introduce the new function to get the number of bits and bytes from an MPI.

Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com>
---
 include/linux/mpi.h       |  2 ++
 lib/crypto/mpi/mpicoder.c | 33 ++++++++++++++++++++++++++-------
 2 files changed, 28 insertions(+), 7 deletions(-)

diff --git a/include/linux/mpi.h b/include/linux/mpi.h
index eb0d1c1db208..a7dd4c9d8120 100644
--- a/include/linux/mpi.h
+++ b/include/linux/mpi.h
@@ -90,6 +90,8 @@ enum gcry_mpi_format {
 };
 
 MPI mpi_read_raw_data(const void *xbuffer, size_t nbytes);
+int mpi_key_length(const void *xbuffer, unsigned int ret_nread,
+		   unsigned int *nbits_arg, unsigned int *nbytes_arg);
 MPI mpi_read_from_buffer(const void *buffer, unsigned *ret_nread);
 int mpi_fromstr(MPI val, const char *str);
 MPI mpi_scanval(const char *string);
diff --git a/lib/crypto/mpi/mpicoder.c b/lib/crypto/mpi/mpicoder.c
index 3cb6bd148fa9..92447a1c8bf9 100644
--- a/lib/crypto/mpi/mpicoder.c
+++ b/lib/crypto/mpi/mpicoder.c
@@ -79,22 +79,41 @@ MPI mpi_read_raw_data(const void *xbuffer, size_t nbytes)
 }
 EXPORT_SYMBOL_GPL(mpi_read_raw_data);
 
-MPI mpi_read_from_buffer(const void *xbuffer, unsigned *ret_nread)
+int mpi_key_length(const void *xbuffer, unsigned int ret_nread,
+		   unsigned int *nbits_arg, unsigned int *nbytes_arg)
 {
 	const uint8_t *buffer = xbuffer;
-	unsigned int nbits, nbytes;
-	MPI val;
+	unsigned int nbits;
 
-	if (*ret_nread < 2)
-		return ERR_PTR(-EINVAL);
+	if (ret_nread < 2)
+		return -EINVAL;
 	nbits = buffer[0] << 8 | buffer[1];
 
 	if (nbits > MAX_EXTERN_MPI_BITS) {
 		pr_info("MPI: mpi too large (%u bits)\n", nbits);
-		return ERR_PTR(-EINVAL);
+		return -EINVAL;
 	}
 
-	nbytes = DIV_ROUND_UP(nbits, 8);
+	if (nbits_arg)
+		*nbits_arg = nbits;
+	if (nbytes_arg)
+		*nbytes_arg = DIV_ROUND_UP(nbits, 8);
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(mpi_key_length);
+
+MPI mpi_read_from_buffer(const void *xbuffer, unsigned int *ret_nread)
+{
+	const uint8_t *buffer = xbuffer;
+	unsigned int nbytes;
+	MPI val;
+	int ret;
+
+	ret = mpi_key_length(xbuffer, *ret_nread, NULL, &nbytes);
+	if (ret < 0)
+		return ERR_PTR(ret);
+
 	if (nbytes + 2 > *ret_nread) {
 		pr_info("MPI: mpi larger than buffer nbytes=%u ret_nread=%u\n",
 				nbytes, *ret_nread);
-- 
2.34.1

