From: umbraticus@prosimetrum.com
To: 9front@9front.org
Subject: Re: [9front] Re: memory(2): mention tsmemcmp
Date: Tue, 04 May 2021 22:40:14 +1200 [thread overview]
Message-ID: <4B6A5210DBF8C513DFF99DAF6C3684A2@prosimetrum.com> (raw)
In-Reply-To: <CABO6shcsCHzF1St2f4WPy0_7Te5Ggumk0MHQFt5SVfeAYzR28g@mail.gmail.com>
Thanks. Just fixed your itses and suggested some
mild improvements to the wording below.
diff -r 47a307f91238 sys/man/2/memory
--- a/sys/man/2/memory Fri Apr 30 00:20:39 2021 +0200
+++ b/sys/man/2/memory Sun May 02 17:20:35 2021 +0300
@@ -1,6 +1,6 @@
.TH MEMORY 2
.SH NAME
-memccpy, memchr, memcmp, memcpy, memmove, memset \- memory operations
+memccpy, memchr, memcmp, memcpy, memmove, memset, tsmemcmp \- memory operations
.SH SYNOPSIS
.B #include <u.h>
.br
@@ -24,6 +24,11 @@
.PP
.B
void* memset(void *s, int c, ulong n)
+.PP
+.B #include <libsec.h>
+.PP
+.B
+int tsmemcmp(void *s1, void *s2, ulong n)
.SH DESCRIPTION
These functions operate efficiently on memory areas
(arrays of bytes bounded by a count, not terminated by a zero byte).
@@ -103,11 +108,22 @@
.IR c .
It returns
.IR s .
+.PP
+.I Tsmemcmp
+is a variant of
+.I memcmp
+that is safe against timing attacks.
+It does not stop when it sees a difference,
+so that its runtime is a function of
+.I n
+and not something that can give an attacker clues.
.SH SOURCE
All these routines have portable C implementations in
.BR /sys/src/libc/port .
Most also have machine-dependent assembly language implementations in
.BR /sys/src/libc/$objtype .
+.I Tsmemcmp
+is found at
+.BR /sys/src/libsec/port/tsmemcmp.c .
.SH SEE ALSO
.IR strcat (2)
.SH BUGS
@@ -124,3 +140,8 @@
and
.I memmove
are handed a negative count, they abort.
+.PP
+.I Memcmp
+should not be used to compare sensitive data,
+as it is vulnerable to timing attacks.
+Instead,
+.I tsmemcmp
+should be used.
next prev parent reply other threads:[~2021-05-04 10:46 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-29 11:40 [9front] " kemal
2021-04-29 16:32 ` [9front] " kemal
2021-05-02 10:51 ` cinap_lenrek
2021-05-02 14:21 ` kemal
2021-05-04 10:40 ` umbraticus [this message]
2021-05-09 13:10 ` cinap_lenrek
2021-05-09 15:25 ` kemal
2021-05-09 16:10 ` hiro
2021-05-09 19:17 ` kemal
2021-05-15 10:40 ` cinap_lenrek
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