linux-kernel - [PATCH 1/3] MIPS: KASLR: Correcte valid bits in apply_r_mips_26

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Date:   Thu, 19 Nov 2020 10:29:12 +0800
From:   Jinyang He <hejinyang@...ngson.cn>
To:     Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        Huacai Chen <chenhc@...ote.com>,
        Jiaxun Yang <jiaxun.yang@...goat.com>
Cc:     linux-mips@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH 1/3] MIPS: KASLR: Correcte valid bits in apply_r_mips_26_rel

Apply_r_mips_26_rel() relocates instructions like j, jal and etc. These
instructions consist of 6bits function field and 26bits address field.
The value of target_addr as follows,
=================================================================
|     high 4bits           |            low 28bits              |
=================================================================
|the high 4bits of this PC | the low 26bits of instructions << 2|
=================================================================
Thus, loc_orig and log_new both need high 4bits ranther than high 6bits.
Replace 0x3ffffff with 0xfffffff.

Signed-off-by: Jinyang He <hejinyang@...ngson.cn>
---
 arch/mips/kernel/relocate.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/mips/kernel/relocate.c b/arch/mips/kernel/relocate.c
index 3d80a51..709cfa0 100644
--- a/arch/mips/kernel/relocate.c
+++ b/arch/mips/kernel/relocate.c
@@ -95,7 +95,7 @@ static int __init apply_r_mips_26_rel(u32 *loc_orig, u32 *loc_new, long offset)

 	/* Original target address */
 	target_addr <<= 2;
-	target_addr += (unsigned long)loc_orig & ~0x03ffffff;
+	target_addr += (unsigned long)loc_orig & ~0x0fffffff;

 	/* Get the new target address */
 	target_addr += offset;
@@ -105,7 +105,7 @@ static int __init apply_r_mips_26_rel(u32 *loc_orig, u32 *loc_new, long offset)
 		return -ENOEXEC;
 	}

-	target_addr -= (unsigned long)loc_new & ~0x03ffffff;
+	target_addr -= (unsigned long)loc_new & ~0x0fffffff;
 	target_addr >>= 2;

 	*loc_new = (*loc_new & ~0x03ffffff) | (target_addr & 0x03ffffff);
-- 
2.1.0