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lib: sbi: Respect scounteren when emulating the time CSR

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This optimization creates a correctness issue, as it prevents supervisor
software from restricting VS-mode or U-mode access to the time CSR for
its own purposes.

Closes: https://github.com/riscv-software-src/opensbi/issues/370
Fixes: ebc8ebc0f8 ("lib: sbi: Improve HPM CSR read/write emulation")
Signed-off-by: Samuel Holland <samuel.holland@sifive.com>
Reviewed-by: Anup Patel <anup@brainfault.org>
This commit is contained in:
Samuel Holland
2024-08-29 13:22:36 -07:00
committed by Anup Patel
parent 00093a2000
commit beef2f6937
1 changed files with 2 additions and 3 deletions
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5
lib/sbi/sbi_emulate_csr.c
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@@ -66,12 +66,11 @@ int sbi_emulate_csr_read(int csr_num, struct sbi_trap_regs *regs,
*csr_val = csr_read(CSR_MCYCLE); *csr_val = csr_read(CSR_MCYCLE);
break; break;
case CSR_TIME: case CSR_TIME:
if (!hpm_allowed(csr_num - CSR_CYCLE, prev_mode, virt))
return SBI_ENOTSUPP;
/* /*
* We emulate TIME CSR for both Host (HS/U-mode) and * We emulate TIME CSR for both Host (HS/U-mode) and
* Guest (VS/VU-mode). * Guest (VS/VU-mode).
*
* Faster TIME CSR reads are critical for good performance
* in S-mode software so we don't check CSR permissions.
*/ */
*csr_val = (virt) ? sbi_timer_virt_value(): *csr_val = (virt) ? sbi_timer_virt_value():
sbi_timer_value(); sbi_timer_value();