| Message ID | 20240829202242.3659520-1-samuel.holland@sifive.com |
|---|---|
| State | Accepted |
| Headers | show |
| Series | lib: sbi: Respect scounteren when emulating the time CSR | expand |
On Fri, Aug 30, 2024 at 1:52 AM Samuel Holland <samuel.holland@sifive.com> wrote: > > 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: ebc8ebc0f846 ("lib: sbi: Improve HPM CSR read/write emulation") > Signed-off-by: Samuel Holland <samuel.holland@sifive.com> LGTM. Reviewed-by: Anup Patel <anup@brainfault.org> Applied this patch to the riscv/opensbi repo. Thanks, Anup > --- > > lib/sbi/sbi_emulate_csr.c | 5 ++--- > 1 file changed, 2 insertions(+), 3 deletions(-) > > diff --git a/lib/sbi/sbi_emulate_csr.c b/lib/sbi/sbi_emulate_csr.c > index 869c81f4..3adec78d 100644 > --- a/lib/sbi/sbi_emulate_csr.c > +++ b/lib/sbi/sbi_emulate_csr.c > @@ -66,12 +66,11 @@ int sbi_emulate_csr_read(int csr_num, struct sbi_trap_regs *regs, > *csr_val = csr_read(CSR_MCYCLE); > break; > 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 > * 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(): > sbi_timer_value(); > -- > 2.45.1 > > > -- > opensbi mailing list > opensbi@lists.infradead.org > http://lists.infradead.org/mailman/listinfo/opensbi
diff --git a/lib/sbi/sbi_emulate_csr.c b/lib/sbi/sbi_emulate_csr.c index 869c81f4..3adec78d 100644 --- a/lib/sbi/sbi_emulate_csr.c +++ b/lib/sbi/sbi_emulate_csr.c @@ -66,12 +66,11 @@ int sbi_emulate_csr_read(int csr_num, struct sbi_trap_regs *regs, *csr_val = csr_read(CSR_MCYCLE); break; 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 * 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(): sbi_timer_value();
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: ebc8ebc0f846 ("lib: sbi: Improve HPM CSR read/write emulation") Signed-off-by: Samuel Holland <samuel.holland@sifive.com> --- lib/sbi/sbi_emulate_csr.c | 5 ++--- 1 file changed, 2 insertions(+), 3 deletions(-)