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target/riscv: mmu changes for zicfiss shadow stack protection

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zicfiss protects shadow stack using new page table encodings PTE.W=1,
PTE.R=0 and PTE.X=0. This encoding is reserved if zicfiss is not
implemented or if shadow stack are not enabled.
Loads on shadow stack memory are allowed while stores to shadow stack
memory leads to access faults. Shadow stack accesses to RO memory
leads to store page fault.

To implement special nature of shadow stack memory where only selected
stores (shadow stack stores from sspush) have to be allowed while rest
of regular stores disallowed, new MMU TLB index is created for shadow
stack.

Furthermore, `check_zicbom_access` (`cbo.clean/flush/inval`) may probe
shadow stack memory and must always raise store/AMO access fault because
it has store semantics. For non-shadow stack memory even though
`cbo.clean/flush/inval` have store semantics, it will not fault if read
is allowed (probably to follow `clflush` on x86). Although if read is not
allowed, eventually `probe_write` will do store page (or access) fault (if
permissions don't allow it). cbo operations on shadow stack memory must
always raise store access fault. Thus extending `get_physical_address` to
recieve `probe` parameter as well.

Signed-off-by: Deepak Gupta <debug@rivosinc.com>
Suggested-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Message-ID: <20241008225010.1861630-14-debug@rivosinc.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>
This commit is contained in:
Deepak Gupta 2024-10-08 15:50:03 -07:00 • committed by Alistair Francis
parent f9fdf9077c
commit 669b486749
2 changed files with 53 additions and 14 deletions
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3
target/riscv/internals.h
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@ -30,12 +30,15 @@
* - U+2STAGE 0b100
* - S+2STAGE 0b101
* - S+SUM+2STAGE 0b110
* - Shadow stack+U 0b1000
* - Shadow stack+S 0b1001
*/
#define MMUIdx_U 0
#define MMUIdx_S 1
#define MMUIdx_S_SUM 2
#define MMUIdx_M 3
#define MMU_2STAGE_BIT (1 << 2)
#define MMU_IDX_SS_WRITE (1 << 3)
static inline int mmuidx_priv(int mmu_idx)
{