Messages in this thread | | | From | David Laight <> | Subject | RE: [PATCH v2] riscv: fix incorrect use of __user pointer | Date | Mon, 27 Nov 2023 10:35:42 +0000 |
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From: Clément Léger > Sent: 27 November 2023 10:24 > > On 25/11/2023 16:37, David Laight wrote: > > ... > >> @@ -491,7 +486,7 @@ int handle_misaligned_load(struct pt_regs *regs) > >> > >> val.data_u64 = 0; > >> for (i = 0; i < len; i++) { > >> - if (load_u8(regs, (void *)(addr + i), &val.data_bytes[i])) > >> + if (load_u8(regs, addr + i, &val.data_bytes[i])) > >> return -1; > >> } > > > > I'd really have thought that you'd want to pull the kernel/user > > check way outside the loop? > > Hi David, > > I hope the compiler is able to extract that 'if' out of the loop since > regs isn't modified in the loop. Nevertheless, that could be more > "clear" if put outside indeed.
If has access regs->xxx then the compiler can't do so because it will must assume that the assignment might alias into 'regs'. That is even true for byte writes if 'strict-aliasing' is enabled - which it isn't for linux kernel builds.
It might do so if 'regs' were 'const'; it tends to assume that if it can't change something nothing can - although that isn't true.
David
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