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[Qemu-riscv] [PATCH 1/2] target/riscv/pmp.c: Don't try further once matc

From: Anup Patel
Subject: [Qemu-riscv] [PATCH 1/2] target/riscv/pmp.c: Don't try further once matching PMP entry found
Date: Wed, 5 Dec 2018 13:57:02 +0530

As-per RISC-V privilege spec, we should only consider first matching
PMP entry. This is not enforced by current pmp_has_access().

Let's say we have two PMP entries configured by M-mode code:
PMP0: 0x0000000080000000-0x000000008001ffff (A)
PMP1: 0x0000000000000000-0xffffffffffffffff (A,R,W,X)

Now if S-mode code tries to access 0x80000000 then it should
generate trap to M-mode because PMP0 blocks the access.

The current implementation of pmp_has_access() checks PMP0 which gives
result=0 so it continues and tries PMP1 which gives result=1 hence
the access to 0x80000000 from S-mode is allowed.

This patch fixes pmp_has_access() to return immediatiely once
a matching entry is found (irrespective to the value of result).

Signed-off-by: Anup Patel <address@hidden>
 target/riscv/pmp.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/target/riscv/pmp.c b/target/riscv/pmp.c
index 3dbb87c69d..936a52b6ba 100644
--- a/target/riscv/pmp.c
+++ b/target/riscv/pmp.c
@@ -193,8 +193,11 @@ bool pmp_has_access(CPURISCVState *env, target_ulong addr, 
int size, int rw,
                 /* breaks iff other covering entries (invalid config). Punt */
                 *tlb_size = roundpow2(ea - sa);
-            goto match;
+        /* only first matching PMP entry applies */
+        if (sa <= addr && (addr + size - 1) < ea)
+            goto match;
     /* only allow M mode if no rules are present */

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