From b03c9f9fdc37dab81ea04d5dacdc5995d4c224c2 Mon Sep 17 00:00:00 2001
From: Edward Cree <ecree@solarflare.com>
Date: Mon, 7 Aug 2017 15:26:36 +0100
Subject: bpf/verifier: track signed and unsigned min/max values
Allows us to, sometimes, combine information from a signed check of one
bound and an unsigned check of the other.
We now track the full range of possible values, rather than restricting
ourselves to [0, 1<<30) and considering anything beyond that as
unknown. While this is probably not necessary, it makes the code more
straightforward and symmetrical between signed and unsigned bounds.
Signed-off-by: Edward Cree <ecree@solarflare.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
---
kernel/bpf/tnum.c | 16 ++++++++++++++++
1 file changed, 16 insertions(+)
(limited to 'kernel/bpf/tnum.c')
diff --git a/kernel/bpf/tnum.c b/kernel/bpf/tnum.c
index 92eeeb1974a2..1f4bf68c12db 100644
--- a/kernel/bpf/tnum.c
+++ b/kernel/bpf/tnum.c
@@ -17,6 +17,22 @@ struct tnum tnum_const(u64 value)
return TNUM(value, 0);
}
+struct tnum tnum_range(u64 min, u64 max)
+{
+ u64 chi = min ^ max, delta;
+ u8 bits = fls64(chi);
+
+ /* special case, needed because 1ULL << 64 is undefined */
+ if (bits > 63)
+ return tnum_unknown;
+ /* e.g. if chi = 4, bits = 3, delta = (1<<3) - 1 = 7.
+ * if chi = 0, bits = 0, delta = (1<<0) - 1 = 0, so we return
+ * constant min (since min == max).
+ */
+ delta = (1ULL << bits) - 1;
+ return TNUM(min & ~delta, delta);
+}
+
struct tnum tnum_lshift(struct tnum a, u8 shift)
{
return TNUM(a.value << shift, a.mask << shift);
--
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