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riscv: lib: uaccess: fix CSR_STATUS SR_SUM bit

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Since commit 5d8544e2d0 ("RISC-V: Generic library routines and assembly")
and commit ebcbd75e39 ("riscv: Fix the bug in memory access fixup code"),
if __clear_user and __copy_user return from an fixup branch,
CSR_STATUS SR_SUM bit will be set, it is a vulnerability, so that
S-mode memory accesses to pages that are accessible by U-mode will success.
Disable S-mode access to U-mode memory should clear SR_SUM bit.

Fixes: 5d8544e2d0 ("RISC-V: Generic library routines and assembly")
Fixes: ebcbd75e39 ("riscv: Fix the bug in memory access fixup code")
Signed-off-by: Chen Lifu <chenlifu@huawei.com>
Reviewed-by: Ben Dooks <ben.dooks@codethink.co.uk>
Link: https://lore.kernel.org/r/20220615014714.1650349-1-chenlifu@huawei.com
Cc: stable@vger.kernel.org
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>
This commit is contained in:
Chen Lifu 2022-06-15 09:47:14 +08:00 committed by Palmer Dabbelt
parent 4d1044fcb9
commit c08b4848f5
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GPG key ID: EF4CA1502CCBAB41
1 changed files with 2 additions and 2 deletions
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4
arch/riscv/lib/uaccess.S
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@ -175,7 +175,7 @@ ENTRY(__asm_copy_from_user)
/* Exception fixup code */
10:
/* Disable access to user memory */
csrs CSR_STATUS, t6
csrc CSR_STATUS, t6
mv a0, t5
ret
ENDPROC(__asm_copy_to_user)
@ -227,7 +227,7 @@ ENTRY(__clear_user)
/* Exception fixup code */
11:
/* Disable access to user memory */
csrs CSR_STATUS, t6
csrc CSR_STATUS, t6
mv a0, a1
ret
ENDPROC(__clear_user)